Ultraviolet Spectroscopy

Size: px
Start display at page:

Download "Ultraviolet Spectroscopy"

Transcription

1 Ultraviolet Spectroscopy The wavelength of UV and visible light are substantially shorter than the wavelength of infrared radiation. The UV spectrum ranges from 100 to 400 nm. A UV-Vis spectrophotometer measures the amount of light absorbed at each wavelength of the UV and visible regions of the electromagnetic spectrum. A UV or visible spectrophotometer has the same basic design as an infrared spectrophotometer. In a standard UV-Vis spectrophotometer, a beam of light is split; one half of the beam (the sample beam) is directed through a transparent cell containing a solution of the compound being analyzed, and one half (the reference beam) is directed through an identical cell that does not contain the compound but contains the solvent. 1Solvents are chosen to be transparent in the region of the spectrum being used for analysis.

2 The instrument is designed so that it can make a comparison of the intensities of the two beams as it scans over the desired region of the wavelengths. If the compound absorbs light at a particular wavelength, the intensity of the sample beam (I S ) will be less than that of the reference beam (I R ). Absorption of radiation by a sample is measured at various wavelengths and plotted by a recorder to give the spectrum which is a plot of the wavelength of the entire region versus the absorption (A) of light at each wavelength. 2

3 A broad absorption band in the region between 210 and 260 nm. The absorption is at a maximum at nm. It is this wavelength that is usually reported in the chemical literature λ max. 3

4 Expressions Used in Ultraviolet Spectrometry The spectrum shows that the scan is from nm. Because absorption by atmospheric carbon dioxide becomes significant below 200 nm, the nm region is usually not scanned unless special air-free techniques are employed. 4

5 The wavelength of absorption is usually reported as λ max which represents the wavelength at the highest point of the curve. The absorption of energy is reported as absorbance (not transmittance as in infrared spectra). The absorbance at a particular wavelength is defined by the equation: The absorbance by a compound at a particular wavelength increases with an increasing number of molecules undergoing transitions. 5

6 Therefore, the absorbance depends on the electronic structure of the compound and also upon the concentration of the sample and the length of the sample cell. Usually, energy absorption is reported as molar absorptivity ε (also called molar extinction coefficient) rather as the actual absorbance. The molar absorptivity (usually reported at λ max ) is a reproducible value that makes into account concentration and cell length. It is simply the proportionality constant that relates the observed absorbance (A) at a particular wavelength (λ) to the molar concentration (c) of the sample and length (l) (in centimeter) of the path of the light beam through the sample cell. 6

7 Absorption of infrared radiation by a molecule leads to increased vibrations of covalent bonds. Molecular transitions from the ground state to an excited state requires about 2-15 kcal/mol. Both UV and visible radiation are of higher energy than IR radiation. Absorption of UV or visible light results in electronic transitions; electrons are promoted from low-energy ground state or orbitals to higher-energy excited-state orbitals. These transitions require about kcal/mol. The energy absorbed is subsequently dissipated as heat, as light (e.g., fluorescence), or in chemical reactions (such as isomerization or free-radical reactions) or in dissociation or ionization of the molecule. 7 The structural unit associated with an electronic transition in the UV-Vis spectroscopy is called a chromophore.

8 The wavelength of UV or visible light absorbed depends on the ease of electron promotion. Molecules that require more energy for electron promotion absorb at shorter wavelengths. Compounds that absorb light in the visible region (that is colored compounds) have more-easily promoted electrons than compounds that absorb at shorter UV wavelengths. 8 colorless

9 Although the energy absorption by a molecule is quantized, a UV or visible spectrum consists of not a spectrum of lines or sharp peaks but rather of broad absorption bands over a wide range of wavelength. The reason for the broad absorption is that the energy levels of both the ground state and the excited state of a molecule are subdivided into rotational and vibrational sublevels. Electronic transitions may occur from any of the sublevels of the ground state to any one of the sublevels of an excited state. That is, a discrete line is not obtained since electronic absorption is superimposed on rotational and vibrational sublevels. Since these various transitions differ slightly in energy, their wavelengths of absorption also differ slightly and give rise to the broad band observed in the spectrum. 9

10 10

11 11

12 Types of Electron Transitions The ground state of an organic molecule contains valence electrons in three principal types of molecular orbitals: sigma (σ) orbitals; pi (π) orbitals; and filled but nonbonded orbitals (n). Both σ and π orbitals are formed from the overlap of two atomic or hybrid orbitals. Each of these molecular orbitals therefore has an antibonding σ* or π* orbital associated with it. An orbital containing n electrons does not have an antibonding orbital (because it was not formed from two orbitals). 12

13 Electron transitions involve the promotion of an electron from one of the three ground states (σ, π, or n) to one of the two excited states (σ, or π ). There are six possible transitions; the four important transitions and their relative energies are: 13

14 The most useful region of the UV spectrum is at wavelengths longer than 200 nm. The following transitions give rise to absorption in the nonuseful nm range: π π* for an isolated double bond, and σ σ* for an ordinary carbon-carbon bond. The useful transitions (200 nm-400 nm) are π π* for compounds with conjugated double bonds, and some n σ* and some n π* transitions. Alkenes and nonconjugated dienes usually have absorption maxima below 200 nm. Example: Ethene gives an absorption maximum at 171 nm, 1,4-pentadiene gives an absorption maximum at 178 nm. 14

15 Absorption by Polyenes Compounds whose molecules contain conjugated multiple bonds have absorption maxima at wavelengths longer than 200 nm. For example, less energy is required to promote a π electron of 1,3- butadiene than is needed to promote a π electron of ethylene. The reason is that the energy gap between the HOMO and the LUMO for conjugated double bonds is less than the energy difference for an isolated double bond. Resonance-stabilization of the excited state of a conjugated diene is one factor that decreases the energy of the excited state. λ max at 171 nm λ max at 217 nm Because less energy is needed for a π π* transition of 1,3-butadiene, this diene absorbs UV radiation of longer wavelengths than does ethylene. 15

16 The UV spectrum of cis,trans-1,3-cyclooctadiene The π π* transition in cis,trans-1,3- cyclooctadiene involves excitation of an electron from the HOMO to LUMO 16

17 Sufficient conjugation shifts the absorption to wavelengths that reach into the visible region of spectrum. The compound responsible for the red color of tomatoes 17 The compound responsible for the color of carrot

18 18

19 General Rule: General Rule: the greater the number of conjugated multiple bonds a compound contains, the longer will be the wavelength at which the compound absorbs light. 19

20 Absorption by Compounds with C=O Bonds The carbonyl groups of saturated aldehydes and ketones give a weak absorption band in the UV region between 270 and 300 nm. Aldehydes and ketones have two absorption bands in the ultraviolet region. Both involve excitation of an electron to an antibonding π* orbital (n π* and π π* ). This band is shifted to longer wavelengths ( nm) when the carbonyl group is conjugated with a double bond. 20

21 21

22 Also, compounds in which the carbon-oxygen double bond is conjugated with a carbon-carbon double bond have absorption maxima corresponding to n π* excitation and π π* excitations. The n π* absorption maxima occur at larger wavelengths but are much weaker (i.e., smaller molar absorptivities) 22

23 Absorption by Aromatic Systems The conjugated π electrons of a benzene ring give characteristic ultraviolet absorptions that indicate the presence of a benzene ring in an unknown compound. Benzene and other aromatic compounds exhibit morecomplex spectra than can be explained by simple π π* transitions. The complexity arises from the existence of several low-lying excited states. One absorption band of moderate intensity occurs near 205 nm and another, less intense band appears in the nm range. Conjugation outside the benzene ring leads to absorptions at other wavelengths. 23

24 24

25 Absorption Arising from Transitions of n Electrons Compounds that contain nitrogen, sulfur, phosphorous, or one of the halogens all have unshared n electrons. If the structure contains no π bonds, these n electrons can undergo only n σ* transitions. Because the n electrons are of higher energy than either σ or π electrons, less energy is required to promote an n electrons, and transitions occur at longer wavelengths than σ σ* transitions. 25

26 The π* orbital is of lower energy than the σ* orbital; consequently, n π* transitions require less energy than n σ* transitions and often are in the range of a normal instrument scan. The n electrons are in a different region of space from σ* and π* orbitals, and the probability of an n transition is low. Since molar absorptivity depends on the number of electrons undergoing transitions, ε values for n transitions are low, in the range (compared to about 10,000 for a π π* transition). A compound such as acetone that contains both a π bond and n electrons exhibits both π π* and n π* transitions. Acetone shows absorption at 187 nm (π π*) and 270 nm (n π*) 26

27 270 nm 187 nm 27

28 Absorption by Alcohols Unless the molecule has other chromophores, alcohols are transparent above about 200 nm. Example: λ max for methanol is 177 nm. Absorption by Ethers and Epoxides Simple ethers have their absorptions maximum at about 185 nm and are transparent to ultraviolet radiation above about 220 nm. 28

29 Absorption by Amines In the absence of any other chromospheres, the UV-Vis spectrum of an alkylamine is not very informative. The longest wavelength absorption involves promoting one of the unshared electrons of nitrogen to an antibonding σ* orbital (n σ*) with a λ max in relatively inaccessible region near 200 nm. In arylamines the interaction of the nitrogen lone pair with the π-electron system of the ring shifts the ring s absorptions to longer wavelengths. Tying up the lone pair by protonation causes the UV-Vis spectrum of anilinium to resemble benzene. 29

30 Absorption by Phenols An OH group affects the UV-Vis spectrum of benzene in a way similar to that of an NH 2 group, but to a smaller extent. In basic solution, in which OH is converted to O _, however, the shift to longer wavelengths exceeds that of an NH 2 group. 30

31 Absorption by Carboxylic Acid and Carboxylic Acid Derivatives In the absence of any additional chromophores, carboxylic acids absorb at a wavelength (210 nm) that is not very useful for diagnostic purposes. The following values are typical for the n π* absorption associated with C=O group of carboxylic acid derivatives. 31

32 32 Analytical Uses of UV-Vis Vis Spectroscopy In practice, ultraviolet spectrometry is limited to conjugated systems for the most part, and UV-Vis spectroscopy can be used in the structure elucidation of organic molecules to indicate whether conjugation is present in a given sample. Although conjugation in a molecule may be indicated by data from IR, NMR, or mass spectrometry, UV-Vis analysis can provide corroborating information. A more widespread use of UV-Vis spectroscopy, however, has to do with determining concentration of an unknown sample. The relationship A = εcl indicates that the amount of absorption by a sample at a certain wavelength is dependent on its concentration. Using calibration curve of λ max versus concentration of standards, concentration of an unknown sample could be determined.

33 Quantitative analysis using UV-Vis spectroscopy is routinely used in biochemical studies to measure the rates of enzymatic reactions (kinetics). The concentration of a species involved in the reaction (as related to its UV-Vis absorbance) is plotted versus time to determine the rate of reaction. UV-Vis spectroscopy is also used in environmental chemistry to determine the concentration of various metal ions (sometimes involving absorption spectra for organic complexes with the metal), as a setection method in HPLC. 33

34 There is an advantage to the selectivity of ultraviolet absorption; characteristic groups may be recognized in molecules of widely varying complexities. A large portion of a relatively complex molecule may be transparent in the ultraviolet so that we may obtain a spectrum similar to that of a much simpler molecules. The absorption results from the conjugated enone portion of the two compounds 34

35 35 THE END

UV-Visible Spectroscopy

UV-Visible Spectroscopy UV-Visible Spectroscopy UV-Visible Spectroscopy What is UV-Visible Spectroscopy? Molecular spectroscopy that involves study of the interaction of Ultra violet (UV)-Visible radiation with molecules What

More information

ULTRAVIOLET/VISIBLE ABSORPTION SPECTROSCOPY

ULTRAVIOLET/VISIBLE ABSORPTION SPECTROSCOPY ULTRAVIOLET/VISIBLE ABSORPTION SPECTROSCOPY Widely used in chemistry. Perhaps the most widely used in Biological Chemistry. Easy to do. Very easy to do wrong. MUJEEB KHAN BASIS SEMINAR 29th April 2009

More information

Organic Spectroscopy. UV - Ultraviolet-Visible Spectroscopy. !! 200-800 nm. Methods for structure determination of organic compounds:

Organic Spectroscopy. UV - Ultraviolet-Visible Spectroscopy. !! 200-800 nm. Methods for structure determination of organic compounds: Organic Spectroscopy Methods for structure determination of organic compounds: X-ray rystallography rystall structures Mass spectroscopy Molecular formula -----------------------------------------------------------------------------

More information

Ultraviolet - Visible Spectroscopy (UV)

Ultraviolet - Visible Spectroscopy (UV) UV Ultraviolet - Visible Spectroscopy (UV) Introduction to Ultraviolet - Visible Spectroscopy 1 (UV) Background Theory UV Absorption of ultraviolet and visible radiation Absorption of visible and ultraviolet

More information

Introduction. Chapter 12 Mass Spectrometry and Infrared Spectroscopy. Electromagnetic Spectrum. Types of Spectroscopy 8/29/2011

Introduction. Chapter 12 Mass Spectrometry and Infrared Spectroscopy. Electromagnetic Spectrum. Types of Spectroscopy 8/29/2011 Organic Chemistry, 6 th Edition L. G. Wade, Jr. Chapter 12 Mass Spectrometry and Infrared Spectroscopy Introduction Spectroscopy is an analytical technique which helps determine structure. It destroys

More information

Practice Problem Set 7 Applications of UV-Vis Absorption Spectroscopy

Practice Problem Set 7 Applications of UV-Vis Absorption Spectroscopy Practice Problem Set 7 Applications of UV-Vis Absorption Spectroscopy 1. π π Transition is the most concenient and useful transition in UV-Vis Spectroscopy. Why? In σ σ* transitions The high energy required

More information

Infrared Spectroscopy 紅 外 線 光 譜 儀

Infrared Spectroscopy 紅 外 線 光 譜 儀 Infrared Spectroscopy 紅 外 線 光 譜 儀 Introduction Spectroscopy is an analytical technique which helps determine structure. It destroys little or no sample (nondestructive method). The amount of light absorbed

More information

Determining the Structure of an Organic Compound

Determining the Structure of an Organic Compound Determining the Structure of an Organic Compound The analysis of the outcome of a reaction requires that we know the full structure of the products as well as the reactants In the 19 th and early 20 th

More information

INFRARED SPECTROSCOPY (IR)

INFRARED SPECTROSCOPY (IR) INFRARED SPECTROSCOPY (IR) Theory and Interpretation of IR spectra ASSIGNED READINGS Introduction to technique 25 (p. 833-834 in lab textbook) Uses of the Infrared Spectrum (p. 847-853) Look over pages

More information

Lecture Topics: I. IR spectroscopy

Lecture Topics: I. IR spectroscopy IR and Mass Spectrometry Reading: Wade chapter 12, sections 12-1- 12-15 Study Problems: 12-15, 12-16, 12-23, 12-25 Key Concepts and Skills: Given an IR spectrum, identify the reliable characteristic peaks

More information

CHAPTER 12 INFRARED SPECTROSCOPY. and MASS SPECTROSCOPY

CHAPTER 12 INFRARED SPECTROSCOPY. and MASS SPECTROSCOPY KOT 222 ORGANIC CHEMISTRY II CHAPTER 12 INFRARED SPECTROSCOPY and MASS SPECTROSCOPY Part I Infrared Spectroscopy What is Spectroscopy? Spectroscopy is the study of the interaction of matter and electromagnetic

More information

DETERMINACIÓN DE ESTRUCTURAS ORGÁNICAS (ORGANIC SPECTROSCOPY) IR SPECTROSCOPY

DETERMINACIÓN DE ESTRUCTURAS ORGÁNICAS (ORGANIC SPECTROSCOPY) IR SPECTROSCOPY DETERMINACIÓN DE ESTRUCTURAS ORGÁNICAS (ORGANIC SPECTROSCOPY) IR SPECTROSCOPY Hermenegildo García Gómez Departamento de Química Instituto de Tecnología Química Universidad Politécnica de Valencia 46022

More information

UV/Vis (Ultraviolet and Visible) Spectroscopy

UV/Vis (Ultraviolet and Visible) Spectroscopy UV/Vis (Ultraviolet and Visible) Spectroscopy Agilent 8453 Diode Array UV-Vis Spectrophotometer Varian Cary 5000 UV-Vis-NIR Spectrophotometer To Do s Read Chapters 13 & 14. Complete the end-of-chapter

More information

Symmetric Stretch: allows molecule to move through space

Symmetric Stretch: allows molecule to move through space BACKGROUND INFORMATION Infrared Spectroscopy Before introducing the subject of IR spectroscopy, we must first review some aspects of the electromagnetic spectrum. The electromagnetic spectrum is composed

More information

13.4 UV/VIS Spectroscopy

13.4 UV/VIS Spectroscopy 13.4 UV/VIS Spectroscopy The spectroscopy which utilizes the ultraviolet (UV) and visible (VIS) range of electromagnetic radiation, is frequently referred to as Electronic Spectroscopy. The term implies

More information

Organic Chemistry Tenth Edition

Organic Chemistry Tenth Edition Organic Chemistry Tenth Edition T. W. Graham Solomons Craig B. Fryhle Welcome to CHM 22 Organic Chemisty II Chapters 2 (IR), 9, 3-20. Chapter 2 and Chapter 9 Spectroscopy (interaction of molecule with

More information

Chapter 14 Conjugated Compounds and Ultraviolet Spectroscopy

Chapter 14 Conjugated Compounds and Ultraviolet Spectroscopy John E. McMurry www.cengage.com/chemistry/mcmurry Chapter 14 Conjugated Compounds and Ultraviolet Spectroscopy Conjugated and Nonconjugated Dienes Compounds can have more than one double or triple bond

More information

Department of Chemistry College of Science Sultan Qaboos University. Topics and Learning Outcomes

Department of Chemistry College of Science Sultan Qaboos University. Topics and Learning Outcomes Department of Chemistry College of Science Sultan Qaboos University Title : CHEM 3326 (Applied Spectroscopy) Credits : 3 Course Format : 2 lectures and 2 tutorials Course Text : Spectrometric Identification

More information

(3)

(3) 1. Organic compounds are often identified by using more than one analytical technique. Some of these techniques were used to identify the compounds in the following reactions. C 3 H 7 Br C 3 H 8 O C 3

More information

13C NMR Spectroscopy

13C NMR Spectroscopy 13 C NMR Spectroscopy Introduction Nuclear magnetic resonance spectroscopy (NMR) is the most powerful tool available for structural determination. A nucleus with an odd number of protons, an odd number

More information

where h = 6.62 10-34 J s

where h = 6.62 10-34 J s Electromagnetic Spectrum: Refer to Figure 12.1 Molecular Spectroscopy: Absorption of electromagnetic radiation: The absorptions and emissions of electromagnetic radiation are related molecular-level phenomena

More information

A is estimated to be about 10 cm for typical organic molecules based on Xray and electron diffraction

A is estimated to be about 10 cm for typical organic molecules based on Xray and electron diffraction Chapter 14 Applications of UV/Vis Molecular Spectroscopy Problems: pick 5 - I don t have any favorites they are very practical, I am more interested in theory from this chapter 14A Magnitudes of Molar

More information

Infrared Spectroscopy and Mass Spectrometry

Infrared Spectroscopy and Mass Spectrometry Infrared Spectroscopy and Mass Spectrometry Introduction It is fundamental for an organic chemist to be able to identify, or characterize, the new compound that he/she has just made. Sometimes this can

More information

SPECTROSCOPY. Light interacting with matter as an analytical tool

SPECTROSCOPY. Light interacting with matter as an analytical tool SPECTROSCOPY Light interacting with matter as an analytical tool Electronic Excitation by UV/Vis Spectroscopy : X-ray: core electron excitation UV: valance electronic excitation IR: molecular vibrations

More information

HOMEWORK PROBLEMS: IR SPECTROSCOPY AND 13C NMR. The peak at 1720 indicates a C=O bond (carbonyl). One possibility is acetone:

HOMEWORK PROBLEMS: IR SPECTROSCOPY AND 13C NMR. The peak at 1720 indicates a C=O bond (carbonyl). One possibility is acetone: HMEWRK PRBLEMS: IR SPECTRSCPY AND 13C NMR 1. You find a bottle on the shelf only labeled C 3 H 6. You take an IR spectrum of the compound and find major peaks at 2950, 1720, and 1400 cm -1. Draw a molecule

More information

Chapter 13 Mass Spectrometry and Infrared Spectroscopy

Chapter 13 Mass Spectrometry and Infrared Spectroscopy Chapter 13 Mass Spectrometry and Infrared Spectroscopy Copyright 2011 The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 Overview of Mass Spectrometry Mass spectrometry

More information

Wave Properties of Electromagnetic Radiation

Wave Properties of Electromagnetic Radiation Wave Properties of Electromagnetic Radiation Two options are available for analytical utility when an analyte interacts with a beam of electromagnetic radiation in an instrument 1. We can monitor the changes

More information

6. 3. Molecular spectroscopy. Unit 6: Physical chemistry of spectroscopy, surfaces and chemical and phase equilibria

6. 3. Molecular spectroscopy. Unit 6: Physical chemistry of spectroscopy, surfaces and chemical and phase equilibria 6. 3 Molecular spectroscopy Spectroscopy in its various forms is a technique with wide applications across many disciplines. From qualitative analysis in toxicology through to quantitative measurements

More information

CHEM1002 Worksheet 4: Spectroscopy Workshop (1)

CHEM1002 Worksheet 4: Spectroscopy Workshop (1) CHEM1002 Worksheet 4: Spectroscopy Workshop (1) This worksheet forms part of the Spectroscopy Problem Solving Assignment which represents 10% of the assessment of this unit. You should use the support

More information

Chapter 13 Spectroscopy NMR, IR, MS, UV-Vis

Chapter 13 Spectroscopy NMR, IR, MS, UV-Vis Chapter 13 Spectroscopy NMR, IR, MS, UV-Vis Main points of the chapter 1. Hydrogen Nuclear Magnetic Resonance a. Splitting or coupling (what s next to what) b. Chemical shifts (what type is it) c. Integration

More information

CHEM 51LB EXP 1 SPECTROSCOPIC METHODS: INFRARED AND NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY

CHEM 51LB EXP 1 SPECTROSCOPIC METHODS: INFRARED AND NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY CHEM 51LB EXP 1 SPECTRSCPIC METHDS: INFRARED AND NUCLEAR MAGNETIC RESNANCE SPECTRSCPY REACTINS: None TECHNIQUES: IR Spectroscopy, NMR Spectroscopy Infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy

More information

Problem Set 6 UV-Vis Absorption Spectroscopy. 13-1. Express the following absorbances in terms of percent transmittance:

Problem Set 6 UV-Vis Absorption Spectroscopy. 13-1. Express the following absorbances in terms of percent transmittance: Problem Set 6 UV-Vis Absorption Spectroscopy 13-1. Express the following absorbances in terms of percent transmittance: a 0.051 b 0.918 c 0.379 d 0.261 e 0.485 f 0.072 A = log P o /P = log1/t = - log T

More information

EXPERIMENT 1: Survival Organic Chemistry: Molecular Models

EXPERIMENT 1: Survival Organic Chemistry: Molecular Models EXPERIMENT 1: Survival Organic Chemistry: Molecular Models Introduction: The goal in this laboratory experience is for you to easily and quickly move between empirical formulas, molecular formulas, condensed

More information

passing through (Y-axis). The peaks are those shown at frequencies when less than

passing through (Y-axis). The peaks are those shown at frequencies when less than Infrared Spectroscopy used to analyze the presence of functional groups (bond types) in organic molecules The process for this analysis is two-fold: 1. Accurate analysis of infrared spectra to determine

More information

Info Note UV-VIS Nomenclature and Units

Info Note UV-VIS Nomenclature and Units Info Note 804: Ultraviolet-visible spectroscopy or ultraviolet-visible spectrophotometry (UV/VIS) involves the spectroscopy of photons in the UV-visible region. It uses light in the visible and adjacent

More information

For example: (Example is from page 50 of the Thinkbook)

For example: (Example is from page 50 of the Thinkbook) SOLVING COMBINED SPECTROSCOPY PROBLEMS: Lecture Supplement: page 50-53 in Thinkbook CFQ s and PP s: page 216 241 in Thinkbook Introduction: The structure of an unknown molecule can be determined using

More information

Spectrophotometry and the Beer-Lambert Law: An Important Analytical Technique in Chemistry

Spectrophotometry and the Beer-Lambert Law: An Important Analytical Technique in Chemistry Spectrophotometry and the Beer-Lambert Law: An Important Analytical Technique in Chemistry Jon H. Hardesty, PhD and Bassam Attili, PhD Collin College Department of Chemistry Introduction: In the last lab

More information

Modern Instrumental Methods of Analysis J.R.Mudakavi Department of Chemical Engineering Indian Institute of Science, Bangalore

Modern Instrumental Methods of Analysis J.R.Mudakavi Department of Chemical Engineering Indian Institute of Science, Bangalore Modern Instrumental Methods of Analysis J.R.Mudakavi Department of Chemical Engineering Indian Institute of Science, Bangalore Module No. #02 Lecture No.# 06 Ultra Violet and Visible Spectrophotometry-2

More information

CHEM 322 Organic Chemistry II - Professor Kathleen V. Kilway

CHEM 322 Organic Chemistry II - Professor Kathleen V. Kilway CHEM 322 Organic Chemistry II - Professor Kathleen V. Kilway "Organic Chemistry" by Maitland Jones, 4th edition Chapter 12 Homework: 1, 2, 4, 5, 6, 7, 15, 16, 17, 19, 21, 24, 26, 28, 29, 30, 38, 39, 44,

More information

MOLECULAR REPRESENTATIONS AND INFRARED SPECTROSCOPY

MOLECULAR REPRESENTATIONS AND INFRARED SPECTROSCOPY MLEULAR REPRESENTATINS AND INFRARED SPETRSPY A STUDENT SULD BE ABLE T: 1. Given a Lewis (dash or dot), condensed, bond-line, or wedge formula of a compound draw the other representations. 2. Give examples

More information

HUMBOLDT-UNIVERSITÄT ZU BERLIN MATHEMATISCH-NATURWISSENSCHAFTLICHE FAKULTÄT I

HUMBOLDT-UNIVERSITÄT ZU BERLIN MATHEMATISCH-NATURWISSENSCHAFTLICHE FAKULTÄT I HUMBOLDT-UNIVERSITÄT ZU BERLIN MATHEMATISCH-NATURWISSENSCHAFTLICHE FAKULTÄT I INSTITUT FÜR PHYSIK Physik von Makromolekülen UV-VIS absorption characterization of (macro)molecular solutions Persons in charge:

More information

Austin Peay State University Department of Chemistry Chem 1111. The Use of the Spectrophotometer and Beer's Law

Austin Peay State University Department of Chemistry Chem 1111. The Use of the Spectrophotometer and Beer's Law Purpose To become familiar with using a spectrophotometer and gain an understanding of Beer s law and it s relationship to solution concentration. Introduction Scientists use many methods to determine

More information

Infrared Spectroscopy: Theory

Infrared Spectroscopy: Theory u Chapter 15 Infrared Spectroscopy: Theory An important tool of the organic chemist is Infrared Spectroscopy, or IR. IR spectra are acquired on a special instrument, called an IR spectrometer. IR is used

More information

electron does not become part of the compound; one electron goes in but two electrons come out.

electron does not become part of the compound; one electron goes in but two electrons come out. Characterization Techniques for Organic Compounds. When we run a reaction in the laboratory or when we isolate a compound from nature, one of our first tasks is to identify the compound that we have obtained.

More information

E35 SPECTROSCOPIC TECHNIQUES IN ORGANIC CHEMISTRY

E35 SPECTROSCOPIC TECHNIQUES IN ORGANIC CHEMISTRY E35 SPECTRSCPIC TECNIQUES IN RGANIC CEMISTRY TE TASK To use mass spectrometry and IR, UV/vis and NMR spectroscopy to identify organic compounds. TE SKILLS By the end of the experiment you should be able

More information

Molecular Spectroscopy

Molecular Spectroscopy Molecular Spectroscopy UV-Vis Spectroscopy Absorption Characteristics of Some Common Chromophores UV-Vis Spectroscopy Absorption Characteristics of Aromatic Compounds UV-Vis Spectroscopy Effect of extended

More information

Colorimetry Extinction coefficient (ε) Lambda max (λ max ) Qualitative vs. quantitative analysis

Colorimetry Extinction coefficient (ε) Lambda max (λ max ) Qualitative vs. quantitative analysis Lab Week 2 - Spectrophotometry Purpose: Introduce students to the use of spectrophotometry for qualitative (what is it) and quantitative (how much is there of it) analysis of biological samples and molecules.

More information

SPECTROPHOTOMETRY. PRINCIPLE AND APPLICATIONS

SPECTROPHOTOMETRY. PRINCIPLE AND APPLICATIONS EUROPEAN UNION GOVERNMENT OF ROMANIA GOVERNMENT OF THE REPUBLIC OF SERBIA Structural Funds 2007-2013 SPECTROPHOTOMETRY. PRINCIPLE AND APPLICATIONS As.dr.ing. ADRIAN EUGEN CIOABLA WORKSHOP 05 06 September

More information

0 10 20 30 40 50 60 70 m/z

0 10 20 30 40 50 60 70 m/z Mass spectrum for the ionization of acetone MS of Acetone + Relative Abundance CH 3 H 3 C O + M 15 (loss of methyl) + O H 3 C CH 3 43 58 0 10 20 30 40 50 60 70 m/z It is difficult to identify the ions

More information

Survival Organic Chemistry Part I: Molecular Models

Survival Organic Chemistry Part I: Molecular Models Survival Organic Chemistry Part I: Molecular Models The goal in this laboratory experience is to get you so you can easily and quickly move between empirical formulas, molecular formulas, condensed formulas,

More information

II cm -1. Carbon hydrogen bonds absorb here. Alkanes absorb cm-1, Akene C-H cm-1 Aromatic C-H shorter and spikey

II cm -1. Carbon hydrogen bonds absorb here. Alkanes absorb cm-1, Akene C-H cm-1 Aromatic C-H shorter and spikey How to Interpret an IR Spectrum The IR may be broken down into 5 distinct regions. I. 3100-3600cm -1. Alcohols, Carboxylic Acids, Amines and Terminal Alkynes absorb here. The shape and exact location of

More information

Chemistry Entrance Examination Topics

Chemistry Entrance Examination Topics Chemistry Entrance Examination Topics 1. General characteristics of the group 6 elements of the main subgroups on the basis of the position in the Periodic table and of atomic structure. Sulfuric acid,

More information

Infrared Spectroscopy

Infrared Spectroscopy Infrared Spectroscopy 1 Chap 12 Reactions will often give a mixture of products: OH H 2 SO 4 + Major Minor How would the chemist determine which product was formed? Both are cyclopentenes; they are isomers.

More information

18 electron rule : How to count electrons

18 electron rule : How to count electrons 18 electron rule : How to count electrons The rule states that thermodynamically stable transition metal organometallic compounds are formed when the sum of the metal d electrons and the electrons conventionally

More information

UV/Vis Spectroscopy. Varka Evi-Maria Ph.D. Chemist AUTH Thessaloniki 2012

UV/Vis Spectroscopy. Varka Evi-Maria Ph.D. Chemist AUTH Thessaloniki 2012 UV/Vis Spectroscopy Varka Evi-Maria Ph.D. Chemist AUTH Thessaloniki 2012 Introduction of Spectroscopy The structure of new synthesised molecules or isolated compounds from natural sources in the lab must

More information

CHEM 51LB: EXPERIMENT 5 SPECTROSCOPIC METHODS: INFRARED AND NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY

CHEM 51LB: EXPERIMENT 5 SPECTROSCOPIC METHODS: INFRARED AND NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY CHEM 51LB: EXPERIMENT 5 SPECTROSCOPIC METHODS: INFRARED AND NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY REACTIONS: None TECHNIQUES: IR, NMR Infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy are

More information

Determination of Molecular Structure by MOLECULAR SPECTROSCOPY

Determination of Molecular Structure by MOLECULAR SPECTROSCOPY Determination of Molecular Structure by MOLEULAR SPETROSOPY hemistry 3 B.Z. Shakhashiri Fall 29 Much of what we know about molecular structure has been learned by observing and analyzing how electromagnetic

More information

for excitation to occur, there must be an exact match between the frequency of the applied radiation and the frequency of the vibration

for excitation to occur, there must be an exact match between the frequency of the applied radiation and the frequency of the vibration ! = 1 2"c k (m + M) m M wavenumbers! =!/c = 1/" wavelength frequency! units: cm 1 for excitation to occur, there must be an exact match between the frequency of the applied radiation and the frequency

More information

Spectrophotometry Practical Lesson on Medical Chemistry and Biochemistry

Spectrophotometry Practical Lesson on Medical Chemistry and Biochemistry Spectrophotometry Practical Lesson on Medical Chemistry and Biochemistry General Medicine Jiřina Crkovská (translated by Jan Pláteník) 2010/2011 1 Spectrophotometry is one of the most widely used instrumental

More information

Analysis of Riboflavin in a Vitamin Pill by Fluorescence Spectroscopy**

Analysis of Riboflavin in a Vitamin Pill by Fluorescence Spectroscopy** Analysis of Riboflavin in a Vitamin Pill by Fluorescence Spectroscopy** Objectives In this lab, you will use fluorescence spectroscopy to determine the mass and percentage of riboflavin in a vitamin pill.

More information

Spectroscopy. SI Base Units

Spectroscopy. SI Base Units Spectroscopy SI Base Units m - meter - length s - second - time kg - kilogram - mass K - kelvin - thermodynamic temperature A - ampere - electric current cd - candela - luminous intensity mol - amount

More information

Chapter 25 The Chemistry of Life: Organic Chemistry. 25.1 Some General Characteristics of Organic Molecules

Chapter 25 The Chemistry of Life: Organic Chemistry. 25.1 Some General Characteristics of Organic Molecules Chapter 25 The Chemistry of Life: Organic Chemistry general characteristics of organic molecules introduction to hydrocarbons alkanes unsaturated hydrocarbons functional groups: alcohols and ethers compounds

More information

Lab #11: Determination of a Chemical Equilibrium Constant

Lab #11: Determination of a Chemical Equilibrium Constant Lab #11: Determination of a Chemical Equilibrium Constant Objectives: 1. Determine the equilibrium constant of the formation of the thiocyanatoiron (III) ions. 2. Understand the application of using a

More information

F. ELECTRONIC SPECTRA OF COORDINATION COMPOUNDS

F. ELECTRONIC SPECTRA OF COORDINATION COMPOUNDS Introduction: F. ELECTRONIC SPECTRA OF COORDINATION COMPOUNDS Transition metal compounds display a wide variety of colors and many of these compounds are used as artist's pigments (e.g., copper phthalocyanine,

More information

VISIBLE SPECTROSCOPY

VISIBLE SPECTROSCOPY VISIBLE SPECTROSCOPY Visible spectroscopy is the study of the interaction of radiation from the visible part (λ = 380-720 nm) of the electromagnetic spectrum with a chemical species. Quantifying the interaction

More information

Experiment 11. Infrared Spectroscopy

Experiment 11. Infrared Spectroscopy Chem 22 Spring 2010 Experiment 11 Infrared Spectroscopy Pre-lab preparation. (1) In Ch 5 and 12 of the text you will find examples of the most common functional groups in organic molecules. In your notebook,

More information

Analytical chemistry year 12

Analytical chemistry year 12 Analytical chemistry year 12 1) Consider the molecule on the right. a) How many sets of peaks are present in the 1 H NMR spectrum? 3 b) How many sets of peaks are present in the 13 C NMR spectrum? 4 c)

More information

Chapter 18 Let there be light Overhead Fig 18-2 problems: 3, 8, 9, 11,13, 17, 20, 21

Chapter 18 Let there be light Overhead Fig 18-2 problems: 3, 8, 9, 11,13, 17, 20, 21 Chapter 18 Let there be light Overhead Fig 18-2 problems: 3, 8, 9, 11,13, 17, 20, 21 18-1 Properties of light We are all familiar with the wave picture of light. For simplicity we diagram a plane polarized

More information

Suggested solutions for Chapter 3

Suggested solutions for Chapter 3 s for Chapter PRBLEM Assuming that the molecular ion is the base peak (00% abundance) what peaks would appear in the mass spectrum of each of these molecules: (a) C5Br (b) C60 (c) C64Br In cases (a) and

More information

Absorption of IR Light

Absorption of IR Light Absorption of IR Light Absorption of IR light causes changes in the vibrational motions of a molecule. The different vibrational modes available to a molecule include stretching and bending modes. The

More information

Advanced GCE Chemistry A

Advanced GCE Chemistry A Advanced GCE Chemistry A Unit F324 Rings, Polymers and Analysis igh banded Candidate Style Answer Introduction CR has produced these candidate style answers to support teachers in interpreting the assessment

More information

UV-Vis Vis spectroscopy. Electronic absorption spectroscopy

UV-Vis Vis spectroscopy. Electronic absorption spectroscopy UV-Vis Vis spectroscopy Electronic absorption spectroscopy Absortpion spectroscopy Provide information about presence and absence of unsaturated functional groups Useful adjunct to IR Determination of

More information

Ultraviolet-Visible (UV-Vis) Spectroscopy Background Information

Ultraviolet-Visible (UV-Vis) Spectroscopy Background Information 1 Ultraviolet-Visible (UV-Vis) Spectroscopy Background Information Instructions for the Operation of the Cary 300 Bio UV-Visible Spectrophotometer See the Thermo OMNIC Help reference on page 49. Ultraviolet-Visible

More information

EXPERIMENT 11 UV/VIS Spectroscopy and Spectrophotometry: Spectrophotometric Analysis of Potassium Permanganate Solutions.

EXPERIMENT 11 UV/VIS Spectroscopy and Spectrophotometry: Spectrophotometric Analysis of Potassium Permanganate Solutions. EXPERIMENT 11 UV/VIS Spectroscopy and Spectrophotometry: Spectrophotometric Analysis of Potassium Permanganate Solutions. Outcomes After completing this experiment, the student should be able to: 1. Prepare

More information

Problem Set 3 Solutions CH332 (SP 06) 1. Skoog problem 15-1 (omit terms (j), (k) and (m)). Draw diagrams as necessary.

Problem Set 3 Solutions CH332 (SP 06) 1. Skoog problem 15-1 (omit terms (j), (k) and (m)). Draw diagrams as necessary. Problem Set 3 Solutions CH332 (SP 06) 1. Skoog problem 15-1 (omit terms (j), (k) and (m)). Draw diagrams as necessary. a) fluorescence Relaxation of an excited state by emission of a photon without a change

More information

Spectroscopy. Biogeochemical Methods OCN 633. Rebecca Briggs

Spectroscopy. Biogeochemical Methods OCN 633. Rebecca Briggs Spectroscopy Biogeochemical Methods OCN 633 Rebecca Briggs Definitions of Spectrometry Defined by the method used to prepare the sample 1. Optical spectrometry Elements are converted to gaseous atoms or

More information

NMR Spectroscopy. Introduction

NMR Spectroscopy. Introduction Introduction NMR Spectroscopy Over the past fifty years nuclear magnetic resonance spectroscopy, commonly referred to as nmr, has become the most important technique for determining the structure of organic

More information

The Fundamentals of Infrared Spectroscopy. Joe Van Gompel, PhD

The Fundamentals of Infrared Spectroscopy. Joe Van Gompel, PhD TN-100 The Fundamentals of Infrared Spectroscopy The Principles of Infrared Spectroscopy Joe Van Gompel, PhD Spectroscopy is the study of the interaction of electromagnetic radiation with matter. The electromagnetic

More information

Radical and Cation Stabilities Radical vs cation stabilities

Radical and Cation Stabilities Radical vs cation stabilities Mass Spectrometry and Free Radicals MS recap Positive mode of Electron Ionization / ESI MS sees charged species (M+, M+), but does not see uncharged (R ) Radical and Cation Stabilities Radical vs cation

More information

2.7 Acids and Bases: The Brønsted-Lowry Definition. Acids and Bases: The Brønsted-Lowry Definition. Acids and Bases: The Brønsted-Lowry Definition

2.7 Acids and Bases: The Brønsted-Lowry Definition. Acids and Bases: The Brønsted-Lowry Definition. Acids and Bases: The Brønsted-Lowry Definition 2.7 Acids and Bases: The Brønsted-Lowry Definition Two frequently used definitions of acidity The Brønsted-Lowry definition Lewis definition Brønsted-Lowry acid A substance that donates a hydrogen ion

More information

Chemistry 201. Quantitative Analysis

Chemistry 201. Quantitative Analysis Chemistry 201 Lecture 4 Quantitative Analysis NC State University Focus on energy The work done in the internal combustion engine is called pressure volume work. For a simple irreversible stroke the work

More information

ANALYSIS OF ASPIRIN INFRARED (IR) SPECTROSCOPY AND MELTING POINT DETERMINATION

ANALYSIS OF ASPIRIN INFRARED (IR) SPECTROSCOPY AND MELTING POINT DETERMINATION Chem 306 Section (Circle) M Tu W Th Name Partners Date ANALYSIS OF ASPIRIN INFRARED (IR) SPECTROSCOPY AND MELTING POINT DETERMINATION Materials: prepared acetylsalicylic acid (aspirin), stockroom samples

More information

EXPERIMENT 5. Molecular Absorption Spectroscopy: Determination of Iron With 1,10-Phenanthroline

EXPERIMENT 5. Molecular Absorption Spectroscopy: Determination of Iron With 1,10-Phenanthroline EXPERIMENT 5 Molecular Absorption Spectroscopy: Determination of Iron With 1,10-Phenanthroline UNKNOWN Submit a clean, labeled 100-mL volumetric flask to the instructor so that your unknown iron solution

More information

Chemistry 111 Lab: Intro to Spectrophotometry Page E-1

Chemistry 111 Lab: Intro to Spectrophotometry Page E-1 Chemistry 111 Lab: Intro to Spectrophotometry Page E-1 SPECTROPHOTOMETRY Absorption Measurements & their Application to Quantitative Analysis study of the interaction of light (or other electromagnetic

More information

Chapter 10 Introduction to Organic Chemistry: Alkanes. Organic Chemistry. 10.1 Organic Compounds. Organic vs. Inorganic.

Chapter 10 Introduction to Organic Chemistry: Alkanes. Organic Chemistry. 10.1 Organic Compounds. Organic vs. Inorganic. Chapter 10 Introduction to Organic Chemistry: Alkanes 10.1 Organic Compounds Organic Chemistry An organic compound is a compound made from carbon atoms. has one or more C atoms. has many H atoms. may also

More information

How to Quickly Solve Spectrometry Problems

How to Quickly Solve Spectrometry Problems How to Quickly Solve Spectrometry Problems You should be looking for: Mass Spectrometry (MS) Chemical Formula DBE Infrared Spectroscopy (IR) Important Functional Groups o Alcohol O-H o Carboxylic Acid

More information

H NMR (proton NMR): determines number and type of H atoms 13. C NMR (proton NMR): determines number and type of C atoms

H NMR (proton NMR): determines number and type of H atoms 13. C NMR (proton NMR): determines number and type of C atoms 14.1 An Introduction to NMR Spectroscopy A. The Basics of Nuclear Magnetic Resonance (NMR) Spectroscopy nuclei with odd atomic number have a S = ½ with two spin states (+1/2 and -1/2) 1 H NMR (proton NMR):

More information

Organic Spectroscopy

Organic Spectroscopy 1 Organic Spectroscopy Second Year, Michaelmas term, 8 lectures: Dr TDW Claridge & Prof BG Davis Lectures 1 4 highlight the importance of spectroscopic methods in the structural elucidation of organic

More information

(v.e. = 7) and S

(v.e. = 7) and S Chapter 6 Chemical Bonding Diatomic Molecules & Lewis Structures - Diatomic molecules include: H, N, O, F, Cl, Br, or I - Lewis proposed that electrons are shared between neighboring atoms and thereby

More information

Organic Spectroscopy 1 Michaelmas Lecture 6 Dr Rob Paton.

Organic Spectroscopy 1 Michaelmas Lecture 6 Dr Rob Paton. rganic Spectroscopy 1 Michaelmas 2011 Lecture 6 Dr ob Paton robert.paton@chem.ox.ac.uk http://paton.chem.ox.ac.uk 1 ecap of Lecture 5 UV-vis Spectroscopy Measures the gaps between electronic energy levels

More information

Reaction Stoichiometry and the Formation of a Metal Ion Complex

Reaction Stoichiometry and the Formation of a Metal Ion Complex Reaction Stoichiometry and the Formation of a Metal Ion Complex Objectives The objectives of this laboratory are as follows: To use the method of continuous variation to determine the reaction stoichiometry

More information

Last Time: Alkanes (C n H 2n+2 ) Last Time: Organic Compounds. Last Time: Intermolecular Forces- BP Increases w/ Increasing Size

Last Time: Alkanes (C n H 2n+2 ) Last Time: Organic Compounds. Last Time: Intermolecular Forces- BP Increases w/ Increasing Size Announcements & Agenda (0/02/07) Welcome Visitors! Please make yourselves comfortable; we will start with a quiz Mid-term grades are only based on lecture I will give you detailed grade sheets on Monday

More information

Chemistry Instrumental Analysis Lecture 28. Chem 4631

Chemistry Instrumental Analysis Lecture 28. Chem 4631 Chemistry 4631 Instrumental Analysis Lecture 28 Gas Chromatography Detectors Gas Chromatography Monitors the column effluent and produces an electrical signal that is proportional to the amount of analyte

More information

Mass Spectrometry. 1. Calculation of Molecular Ion or Fragment Composition

Mass Spectrometry. 1. Calculation of Molecular Ion or Fragment Composition Mass Spectrometry 1 alculation of Molecular Ion or Fragment omposition a ommon Isotopes Nominal Abundance, Isotope Mass % Exact Mass 1 1 99985 10078 (or D) 0015 0141 1 1 989 10000 13 13 11 130034 14 N

More information

Chapter 2 Polar Covalent Bonds; Acids and Bases

Chapter 2 Polar Covalent Bonds; Acids and Bases John E. McMurry http://www.cengage.com/chemistry/mcmurry Chapter 2 Polar Covalent Bonds; Acids and Bases Javier E. Horta, M.D., Ph.D. University of Massachusetts Lowell Polar Covalent Bonds: Electronegativity

More information

Photosynthesis - Exercise 6 Objectives

Photosynthesis - Exercise 6 Objectives The purpose of this lab exercise will be to examine several factors involved in photosynthesis. -The effect of the intensity of light (# of photons per time) on the rate of photosynthesis and know how

More information

Covalent Bonding SLO 4/14/16. Students will be able to draw Lewis Dot Structures of Covalent Compounds and explain resonance structures.

Covalent Bonding SLO 4/14/16. Students will be able to draw Lewis Dot Structures of Covalent Compounds and explain resonance structures. Covalent Bonding SLO 4/14/16 Students will be able to draw Lewis Dot Structures of Covalent Compounds and explain resonance structures. Classwork Check! Written Assignment: pg. 225, #1, 3, 4, 5, 6 1. Molecular

More information

Chapter 8 Molecules. Some molecular bonds involve sharing of electrons between atoms. These are covalent bonds.

Chapter 8 Molecules. Some molecular bonds involve sharing of electrons between atoms. These are covalent bonds. Chapter 8 Molecules (We have only three days for chapter 8!) 8.1 The Molecular Bond A molecule is an electrically neutral group of atoms held together strongly enough to behave as a single particle. A

More information

Nuclear Magnetic Resonance Spectroscopy

Nuclear Magnetic Resonance Spectroscopy Nuclear Magnetic Resonance Spectroscopy Nuclear magnetic resonance spectroscopy is a powerful analytical technique used to characterize organic molecules by identifying carbonhydrogen frameworks within

More information

Solving Spectroscopy Problems

Solving Spectroscopy Problems Solving Spectroscopy Problems The following is a detailed summary on how to solve spectroscopy problems, key terms are highlighted in bold and the definitions are from the illustrated glossary on Dr. Hardinger

More information