13.1 Carbon: The Scope of Organic Chemistry. Carbon-Carbon bonding is the essential feature. Functional Groups lend diverse chemistry.

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1 Chapter 13 Notes ORGANIC CHEMISTRY is the chemistry of compounds primarily containing the elements C, H, N, O. In most compounds C is the central element. In this chapter we will learn: STRUCTURES and NOMENCLATURE. We shall not study reactions Carbon: The Scope of Organic Chemistry. Carbon-Carbon bonding is the essential feature. Functional Groups lend diverse chemistry. Functional Groups and Size are both principles of organization for organic molecules. We shall pay less attention than your book to the larger organic molecules, called polymers. 1

2 13.2 Alkanes are Saturated Hydrocarbons General Formula: C n H 2N+2 Structures: Carbon Forms 4 covalent single bonds. No multiple bonds. 4 single bonds means Tetrahedral C-bonding with bond angles of ~109.5 Most Figures adapted from copyright 2005, 2006 Brooks Cole. Some figures adapted from: copyright Education How can carbon form four equal bonds? The concept of Hybrid Bonds Pearson free rotation is a property of C-C single bonds Hybrid Bonds form when Hybrid Orbitals overlap. A hybrid orbital is a combination of atomic orbitals, s, p, d etc. 2

3 Figures adapted from: copyright 2005, 2006 Brooks Cole 3

4 Drawing Organic Molecules: Drawing explicitly tetrahedral Carbon. Models help. 4

5 Drawing Organic Molecules: Alkanes can be either straight -chain or branched - chain. Straight -chain examples 5

6 Straight chain s aren t so straight, eh? Conformers Branched -chain example: isobutane Structural Isomers Butane (or n-butane) and isobutene are Structural Isomers: Same number of carbons and hydrogens but different C-C connectivities. 6

7 Example Problems. 1. Draw the Lewis-Structure, condensed structure and carbon-skeleton of n-nonane. Number the carbon chain. 2. Identify the longest chain in an organic molecule. Number it correctly. 3. Are these structures identical or structural isomers, or neither. 7

8 Naming Alkanes base is ane Prefix is meth-, eth-, etc Complete name: Prefix + ane Prefix describes how many C-atoms in the molecular base-name. Straight-chain alkanes are designated normal, with an n preceding the name Branched-chain alkanes have other designations that precede the name like the iso in isobutene (above) Memorization, although the lowest form of learning probably works best here. 8

9 Naming branched-chain alkanes. Name This! 1. Identify the Parent Structure: Trace the longest backbone chain for the PREFIX name, as for n-alkanes. 2. Identify Substituents: If alkane groups appear as substituents the substituent is named as PREFIX+YL, methyl, ethyl, etc (alkyl groups) 3. Numbering: Longest chain carbon numbering starts at the terminus closest to the branching. Minimize branched carbon (s') number (s). 4. When there are multiple substituents specify the carbon number for each substituent before its name. Use di-(2), tri-(3), tetra-(4), etc to indicate the # of identical substituents. 5.The complete compound name assembles as: [substituent carbon number] + [(di-,tri-, etc) substituent group name] + [alkane root name] 9

10 Playing structures with n-hexane and naming them. Substituent naming priority. 10

11 Cycloalkanes (cyclic alkanes) there are no carbon terminii General Formula: C n H 2n Structures: Naming: prefix = cyclo Drawing cyclic structures. Cyclohexane isn t planar at all. 11

12 13.3 Alkenes and Alkynes ALKENES ALKYNES 12

13 Drawing Structures of Alkenes and Alkynes. sp 2 hybridized carbon sp-hybridized carbon Lewis/Kekule Condensed Carbon Skeleton 13

14 Chemical Reactivities of Alkenes and Alkynes: Addition across the multiple bond Isomers of Alkenes and Alkynes. 1. Same kind of structural isomers (branched chain) as in Alkanes. Examples: 2. Structural isomers in which any two (or more) molecules have their multiple bond(s) in different positions in the molecule. (The molecular formula is still identical however). Examples 14

15 3. Stereoisomers in alkenes only. CIS-TRANS isomers. These have different orientations (arrangements) around the double bond. Naming Alkenes (double bonds) and Alkynes (triple bonds) Alkenes (olefins); poly-enes (more than one multiple bond in a molecule). Molecules containing double [=] bonds. Formula: C n H 2n In Alkenes 4-Cs and longer one must specify [=] position. Naming follows the alkane rules, generally (see 4. for numbering) Root+ene and cis-root+ene (trans)-root+ene 1. Meth+ene = Methene doesn't exist,eh? 2. Eth+ene = Ethene 3. Prop+ene = Propene (only 1 isomer) 15

16 4. But+ene = Butene 3 structural isomers; 1-butene, 2-butene & isobutene 2 stereoisomers: cis-2-butene and trans-2-butene. As in alkanes longest chain numbering: Priority is locating the double bond C #1 is the terminus closest to the double bond. Double bond position is specified by the number of 1 st Carbon in the double bond. Substituent positions are indicated by the carbon number of each, as in alkanes. 5. Hex+ene = Hexene (n-hexene: 5 total isomers: 3 structural isomers. 4 stereoisomers ) There are branched-chain isomers also. 16

17 Alkynes: triple bond: Naming like alkenes, except with yne suffix. Alkynes: Molecules containing Triple [ ] bonds. Formula: C n H 2n-2 In Alkynes 4-Cs and longer one must specify [ ] position. Naming follows the alkane & alkene rules, generally (see 4. for numbering) Root+yne No cis or trans here. 1. Meth+yne = Methyne, does not exist, eh? 2. Eth+yne = Ethyne 3. Prop+yne = Propyne 4. But+yne = Butyne (2 geometrical isomers) (there is no isobutyne ) As in alkenes longest chain numbering: Priority is locating the triple bond C #1 is the terminus closest to the triple bond. Triple bond position is specified by the number of 1 st Carbon in the triple bond. Substituent positions are indicated by the carbon number of each, as in alkanes. 5. Hexyne (several structural isomers due to triple bond placement and branching) 17

18 13.4 Aromatic Compounds The prototype: Benzene = C 6 H 6 Aryl groups Pi-bonding is unique. Drawing Aromatics: Structural Equivalences 18

19 Labeling & Naming: The ring carbons are numbered or named for substituents. Naming: systematic base name is benzene ; common names common Prefix is a substituent-like alkanes, alkenes, or as for other substituents. benzene ring phenyl Ring: Toluene Xylenes Names of other common benzene derivatives: Choose the base name. 19

20 Polycyclic Aromatic Hydrocarbons (PAHs) 13.5 Amines: Derivatives of Ammonia with alkyl, Aryl substituent(s) Naming: base name is amine; Prefix is the name of the substituents. If the substituents are not identical, they are named in alphabetical order. Methylamine Dimethylamine Trimethylamine 20

21 13.6 Alcohols Contain the OH group (hydroxyl group), as in the formula: R-OH. The alcohol functional group. Propanol and lower are miscible in water. Structures and Names. Naming: Simple alkane alcohols: base name is ol. Prefix is the alkane it derives from, in common or systematic form. Name deives from the longest chain with the hydroxyl carbon. Longest chain name+ol Methylalcohol Ethylalcohol propylalcohol Iso-propylalcohol Methanol Ethanol n-propanol iso-propanol (2 ) Structures: Derivatives of water, eh? Structural Isomers and more naming. By example. Number the position of the OH group. 1-pentanol 2-pentanol 3-pentanol Name this and this and write their skeleton structures CH 2 (OH)-CH 2 -CH(CH 3 )-CH 3 CH 3 -CH(Cl)-CH 2 -CH(OH)-CH 3 21

22 13.6 Ethers Formula: R 1 -O-R 2 Primarily Common Names are used. Common Naming: (R 1 group name) (R 2 group name) ether Order is alphabetical for the groups Name these: CH 3 -O-CH 3 CH 3 CH 2 -O-CH 3 CH 3 OCH 3 The structure is a derivative of water, also. But ethers are not very water soluble Compounds with Carbonyl groups: C=O Aldehyde Ketone Carboxylic Acid Ester Amide 22

23 Supplement: Additional Information about Naming Substituted Benzenes. IUPAC Preferred: (i) Base Name is benzene (ii) Naming substituents is like alkanes (alphabetical) (iii) Numbering ring minimizes the number total of the carbons carrying the substituent. Only these 3 common names for substituted benzenes are preferred by IUPAC. (i) phenol (ii) benzaldehyde (iii) benzoic acid. Although other common names (like toluene) may be used, the are not IUPAC primary preferred. Other common substituted benzenes. 23

24 N aming Examples 24

25 Stereoisomerism. OPTICAL ISOMERS: A pair of non-superimposable mirror image molecules are optical isomers. They are called ENANTIOMERS. Pg 753. Enantiomers have identical carbon-carbon connectivities. An enantiomer is OPTICALLY ACTIVE and is said to be CHIRAL (or a chiral molecule). A tetrahedral carbon with four different substituent groups is a CHIRAL CENTER, or CHIRAL ATOM (Carbon). Pg 753. An equimolar mixture of both optical isomers is called a RACEMIC MIXTURE. Non-superimposable mirror images; Enantiomers: 25

26 Measuring Optical Activity. Physical properties of individual optical isomers (enantiomers) are almost always identical, but some properties are not: rotation of plane-polarized light; chemical reactivity in chiral environments (chiral selectivity). Pure enantiomer drugs like ClaritinD tm. Rotation of Plane-Polarized Light: Dextrorotatory (d-isomer) Levorotatory (l-isomer) Differential Reactivity or Pharmacology (drug efficacy) of individual optical isomers resulted in marketing optically pure drugs (consist of only 1 enantiomer). 26

27 Characterizing Chiral molecules through their SPECIFIC CONFIGURATION. Designated by R, S. Chiral Carbons are bonded to four different groups. Rule 1: Each group has a different PRIORITY. A. The order of priority depends on the Atomic Number of the atoms directly bonded to the chiral C. Highest priority is given to the atom with the largest At. No. B. Orient (rotate) the molecule so that the lowest priority group points away. C. If the path of sequentially decreasing priority for the remaining three visible groups is clockwise (to the right) then the specific configuration is R. If the path of sequentially decreasing priority for the remaining three visible g roups is counter-clockwise (to the left) then the specific configuration is S. Assign specific configuration to the two enantiomers above. 27

28 Rule 2: If Rule 1 cannot decide the relative priority, then use the second atom in the groups;.then use the third atom, etc. Examples Rule 3. Double and triple bond groups 28