IR Summary - All numerical values in the tables below are given in wavenumbers, cm -1. sp 2 C-X double bonds not very useful

Transcription

1 Beauchamp Spectroscopy Tables Infrared Tables (short summary of common absorption frequencies) The values given in the tables that follow are typical values. Specific bands may fall over a range of wavenumbers, cm -. Specific substituents may cause variations in absorption frequencies. Absorption intensities may be stronger or weaker than expected, often depending on dipole moments. Additional bands may confuse the interpretation. In very symmetrical compounds there may be fewer than the expected number of absorption bands (it is even possible that all bands of a functional group may disappear, i.e. a symmetrically substituted alkyne!). Infrared spectra are generally informative about what functional groups are present, but not always. The and 3 M s are often just as informative about functional groups, and sometimes even more so in this regard. Information obtained from one spectroscopic technique should be verified or expanded by consulting the other spectroscopic techniques. I Summary - All numerical values in the tables below are given in wavenumbers, cm - Bonds to arbon (ing wave numbers) sp 3 - single bonds sp 2 - single bonds not used sp 2 - double bonds not very useful alkoxy - not very useful sp - triple bonds acyl and phenyl expanded table on next page Stronger dipoles produce more intense I bands and weaker dipoles produce less intense I bands (sometimes none). Bonds to ydrogen (ing wave numbers) sp primary 2 (two bands) secondary - (one band) amides = strong, amines = weak sp (see sp 2 - bend sp 3 - patterns below) (sp - bend 620) alcohol acid aldehyde - (two bands) S (very weak) thiol S- Z:\classes\spectroscopy\all spectra tables for web.d

2 Beauchamp Spectroscopy Tables 2 arbonyl ighlights (ing wave numbers) Aldehydes Ketones Esters Acids saturated = 725 conjugated = 690 aromatic = 700 saturated = 75 conjugated = 680 aromatic = atom ring = 75 5 atom ring = atom ring = atom ring = 850 ' saturated = 735 conjugated = 720 aromatic = atom ring = atom ring = atom ring = 840 saturated = 75 conjugated = 690 aromatic = 690 Amides Anhydrides Acid hlorides 2 saturated = 650 conjugated = 660 aromatic = atom ring = atom ring = atom ring = atom ring = 850 saturated = 760, 820 conjugated = 725, 785 aromatic = 725, atom ring = 750, atom ring = 785, 865 l saturated = 800 conjugated = 770 aromatic = 770 nitro asymmetric = symmetric = Very often there is a very weak = overtone at approximately 2 x ν ( 3400 cm - ). Sometimes this is mistaken for an or peak., alkene substitution pattern sp 2 - bend patterns for alkenes descriptive alkene term monosubstituted alkene cis disubstituted alkene trans disubstituted alkene geminal disubstituted alkene trisubstituted alkene tetrasubstituted alkene absorption frequencies (cm - ) due to sp 2 bend (broad) none aromatic substitution pattern sp 2 - bend patterns for aromatics descriptive aromatic term monosubstituted aromatic ortho disubstituted aromatic meta disubstituted aromatic para disubstituted aromatic absorption frequencies (cm - ) due to sp 2 bend (sometimes) Aromatic compounds have characteristic weak overtone bands that show up between cm - ). Some books provide pictures for comparison (not here). A strong = peak will cover up most of this region. Z:\classes\spectroscopy\all spectra tables for web.d

3 Beauchamp Spectroscopy Tables 3 units = cm sp - sp 2 - sp 3 - thiol S- = = sp 3 - bend alkene sp 2 - bend mono trans cis alcohol - aldehyde - = alkene acyl - phenol - alkoxy - geminal tri carboxylic acid - = aromatic aromatic sp 2 - bend o bend mono ortho 2 o - nitro nitro meta para expansion of alkene & aromatic sp 2 - bend region (units = cm - ) mono trans mono geminal tri cis alkene sp 2 - bend mono mono meta ortho meta meta aromatic sp 2 - bend para expansion of carbonyl (=) region (units = cm - ) Saturated = lies at higher cm - = in samll rings lies at higher cm - carboxylic acid = (also acid "") ester = (also acyl - and alkoxy -) aldehyde = (also aldehyde -) onjugated = lies at lower cm - ketone = (nothing special) acid chloride = (high =, peak) amide = (low =, amide -) anhydride = anhydride = (high =, 2 peaks) Z:\classes\spectroscopy\all spectra tables for web.d

4 Beauchamp Spectroscopy Tables 4 I Flowchart to determine functional groups in a compound (all values in cm - ). has = band ( cm - ) very strong I Spectrum does not have = band aldehydes (saturated) (unsaturated) aldehyde - ketones (both weak) (saturated) (unsaturated) (rings: higher in small rings) esters - rule of (saturated) (unsaturated) (higher in small rings) acyl (acyl, strong) alkoxy (000-50, alkoxy, medium) acids (saturated) (unsaturated) (higher in small rings) acyl acid amides o 2 o acid chlorides anhydrides acyl (acyl, strong) , very broad (overlaps - ) (saturated) 745 (in 4 atom ring) 3350 & 380, two bands for o amides, one band for 2 o amides, stronger than in amines, extra overtone sometimes at bend, , stronger in amides than amines 800 (saturated) 770 (unsaturated) 760 & 820 (saturated) (unsaturated) two strong bands (acyl, strong) sometimes lost in sp 3 peaks Inductive pull of l increases the electron density between and. nitriles 2250 sharp, stronger than alkynes, a little lower when conjugated alkynes sp - sp - bend 250 (variable intensity) not present or weak when symmetrically substituted, a little lower when conjugated 3300 sharp, strong 620 All I values are approximate and have a range of possibilities depending on the molecular environment in which the functional group resides. esonance often modifies a peak's position because of electron delocalization (= lower, acyl - higher, etc.). I peaks are not 00% reliable. Peaks tend to be stronger (more intense) when there is a large dipole associated with a vibration in the functional group and weaker in less polar bonds (to the point of disappearing in some completely symmetrical bonds). Alkene sp 2 - bending patterns monosubstituted alkene ( , ) geminal disubstituted ( ) cis disubstituted ( ) trans disubstituted ( ) trisubstituted ( ) tetrasubstituted (none, no sp 2 -) Aromatic sp 2 - bending patterns monosubstituted ( , ) ortho disubstituted ( ) meta disubstituted ( ,sometimes, , ) para disubstituted ( ) There are also weak overtone bands between 660 and 2000, but are not shown here. You can consult pictures of typical patterns in other reference books. If there is a strong = band, they may be partially covered up. alkanes sp sp 3 - bend 460 & 380 not useful alkenes sp sp 2 - bend weak or not present aromatics alcohols alcohol (uncertain) ethers alkoxy 20 (alphatic) 040 & 250 (aromatic) nitro compounds , asymmetric (strong) , symmetric (medium) carbon-halogen bonds (see table for spectral patterns) sp (see table), sp 2 - bend overtone patterns between & 480 can be weak alkoxy thiols thiol S amines o 2 o (3 o > 2 o > o ) 2550 (weak) (easy to overlook) , two bands for o amines, one band for 2 o amines, weaker than in amides, - bend, , stronger in amides than amines usually not very useful = F, l, Br, I Z:\classes\spectroscopy\all spectra tables for web.d

5 Beauchamp Spectroscopy Tables 5 deshielding side = less electron rich (inductive & resonance) typical proton chemical shifts arbon and/or heteroatoms without hydrogen do not appear here, but influence on any nearby protons may be seen in the chemical shifts of the protons. and 3 M chemical shift values. 5 alcohol amide - shielding side = more electron rich (inductive & resonance) 2 amine - 6 S thiols, sulfides amines = F,l,Br,I allylic - 2 carboxylic acid - 0 aldehyde aromatic - 6 alkene alcohols ethers esters benzylic - carbonyl alpha epoxide simple sp 3 - > 2 > thiol S PPM typical carbon-3 chemical shifts ketones no 95 halogen with & without F l Br I 5-45 amines, amides with & without aldehydes with carboxylic acids anhydrides esters amides acid chlorides no with & without no 0 with & without alcohols, ethers, esters with & without epoxides with & without simple sp 3 carbon > > 2 > 3 with & without S thiols, sulfides with & without PPM Z:\classes\spectroscopy\all spectra tables for web.d

6 Beauchamp Spectroscopy Tables 6 alculation of chemical shifts for protons at sp 3 carbons α β γ Estimation of sp 3 - chemical shifts with multiple substituent parameters for protons within 3 's of consideration. α = directly attached substituent, use these values when the hydrogen and substituent are attached to the same carbon β = once removed substituent, use these values when the hydrogen and substituent are on adjacent (vicinal) carbons γ = twice removed substituent, use these values when the hydrogen and substituent have a,3 substitution pattern = substituent α β γ - (alkyl) =- (alkenyl) (alkynyl) Ar- (aromatic) F- (fluoro) l- (chloro) Br- (bromo) I- (iodo) (alcohol) (ether) epoxide =- (alkenyl ether) Ar- (aromatic ether) (ester, oxygen side) Ar 2 - (aromatic ester, oxygen side) ArS 3 - (aromatic sulfonate, oxygen) (amine nitrogen) (amide nitrogen) (nitro) S- (thiol, sulfur) S- (sulfide, sulfur) (aldehyde) (ketone) Ar- (aromatic ketone) (carboxylic acid) (ester, carbon side) (amide, carbon side) l- (acid chloride) (nitrile) S- (sulfoxide) S 2 - (sulfone) a. methine b. methylene Starting value and equations for 3 's 3 = α 3 α 3 = (β + γ) is the summation symbol for all substituents considered Starting value and equation for 2 's In a similar manner we can calculate chemical shifts for methylenes ( 2 ) using the following formula 2 =.2 + (α +β + γ) Starting value and equation for 's α β In a similar manner we can calculate chemical shifts for methines () using the following formula =.5 + (α +β + γ) 3 is the summation symbol for all substituents considered β α is the summation symbol for all substituents considered γ β γ γ d. methyl c. methyl e. methylene f. methylene a. methyl = (.5) α + (0.) γ = 2.5 ppm actual = 2.6 b. methylene =.2 + (.5) α + (0.4) β + (0.3) β = 3.4 ppm actual = 3.0 and 3.2 c. methine =.5 + (.4) α + (2.3) α + (0.2) β = 5.4 ppm actual = 5.2 d. methyl = (0.) α =.0 ppm actual =.0 e. methylene =.2 + (0.3) α =.5 ppm actual =.7 f. methylene =.2. + (.7) α = 2.9 ppm actual = 2.9 Z:\classes\spectroscopy\all spectra tables for web.d

7 Beauchamp Spectroscopy Tables 7 Estimated chemical shifts for protons at alkene sp 2 carbons Substituent α geminal α cis α trans ydrogen Alkyl Benzyl alomethyl ()/ alkoxymethyl () 2 / aminomethyl α-keto α-cyano 2 = Alkenyl Phenyl F Fluoro l hloro Br Bromo I Iodo akoxy (ether) ester () 2 / amino amide itro S Thiol Aldehyde Ketone acid ester amide itrile Substitution relative to calculated "" cis Example alculation 3 trans gem (ppm) = α gem + α cis + α trans gem trans cis gem = = 6.6 actual = 6.6 b trans = = 5. actual = 5. a cis = = 5.7 actual = 5.6 c d e f a = (-0.4) = 4.8 actual = 4.9 (J = 4,.6 z) b = (-0.6) = 4.6 actual = 4.6 (J = 6,.6 z) c = = 7.3 actual = 7.4 (J = 4, 6 z) d = = 6.0 actual = 6.2 (J = 8, z) e = = 5.7 actual = 5.8 (J =,.4 z) f = = 6.2 actual = 6.4 (J = 8,.4 z) Z:\classes\spectroscopy\all spectra tables for web.d

8 Beauchamp Spectroscopy Tables 8 Estimated chemical shifts for protons at aromatic sp 2 carbons Substituent α ortho α meta α para ydrogen Methyl l holromethyl l alomethyl ydroxymethyl 2 = Alkenyl Phenyl F Fluoro l hloro Br Bromo I Iodo ydroxy Alkoxy ester () 2 / amino amide itro S thiol/sulfide Aldehyde Ketone acid ester amide itrile Substitution relative to calculated "" para meta meta ortho ortho (ppm) = α ortho + α meta + α para Example alculation ( 3 ) = = 3.7 actual = (2) = (-0.5) ortho + (-0.) para = 6.7 actual = (3) = (-0.2) ortho + (-0.4) para = 6.7 actual = ( 2 ) =.2 + (0.8)α + (.4)α = 3.4 actual = (5) = (0.7) gem = 5.9 actual = (6) = (-0.2) trans = 5.0 actual = (7) = (-0.2) cis = 5.0 actual = 5. Z:\classes\spectroscopy\all spectra tables for web.d

9 Beauchamp Spectroscopy Tables 9 eal Examples of ombination Effects on hemical Shifts π bond anisotropy 0.8 shielded ( 2 ) electronegativity and π bond electronegative substituent and distance from protons l 3 2 l l l multiple substituents 4 3 l 2 l 2 l3 l = = = =?? (oops) substituents at methyl ( 3 ), methylene ( 2 ) and methine () 3 l 3 2 l ( 3 ) 2 l 3 sp - Ar deshielded alcohol = -5 Ar phenol = 4-0 S thiol = -2.5 Ar aromatic thiol = σ bond example too hydrogen bonding 0.8, shielded.5 Ph shielding cone from σ bond 5, hydrogen bonded enol 3 amine = -5 enol = 0-7 amide = acid = 0-3 Ph ( 3 ) 2 Ph alkene substituent resonance and inductive effects aromatic resonance and inductive effects π bond anisotropy produces deshielding Extra electron density via resonance produces Withdrawal of electron density via resonance effect on aromatic shielding effect on aromatic protons, especially produces deshielding effect on aromatic protons, protons. at ortho/para positions. especially at ortho/para positions. Z:\classes\spectroscopy\all spectra tables for web.d

10 Beauchamp Spectroscopy Tables 0 Proton chemical shifts of hydrogen on sp 3 carbons depend on two main factors (electronegativity and pi bond anisotropy). All values listed below are only approximate and have a small plus or minus range about the listed value. All things being equal, methine protons () have greater chemical shifts than methylene protons ( 2 ) which have greater chemical shifts than methyl protons ( 3 )..5 ppm.2 ppm 0.9 ppm methine protons methylene protons methyl protons hemical shifts in an only "alkane" environment.. sp 3 - Electronegative atoms in the vicinity of hydrogen deshield protons and produce a larger chemical shift. If the electronegative atom is in resonance with an adjacent pi system that further withdraws electron density, the chemical shift is increased. a. next to a halogen F l ppm ppm ppm ppm fluoro alkanes chloro alkanes bromo alkanes iodo alkanes b. next to a oxygen Br ppm ppm ppm ppm ppm ppm alcohol alkyl ether aromatic ether alkyl ester aromatic ester epoxide ether (resonance withdrawal) (oxygen side) (oxygen side) (resonance withdrawal) (resonance withdrawal) c. next to a sulfur or nitrogen S S I ppm thiol ppm alkyl ether ppm amines ppm (resonance withdrawal) amides 2. sp 3 - Pi bonds in the vicinity of hydrogen also deshield protons via pi bond anisotropy and produce a larger chemical shift. The closer the sp 3 - is to the pi bond the greater chemical shift observed. When an electronegative atom is part of the pi bond, the chemical shift also increases ppm aldehydes, ketones, carboxylic acids, amides, alkyl ester (oxygen side) ppm aromatic ketones (resonance withdrawal) l ppm acid chlorides (resonance withdrawal) ppm nitro compounds (resonance withdrawal) ppm propargylic protons ppm allylic protons ppm benzylic protons Z:\classes\spectroscopy\all spectra tables for web.d

11 Beauchamp Spectroscopy Tables 3. sp 2 - ydrogens at the side of a pi bond are deshielded even more than above via pi bond anisotropy. An aldehyde produces the largest effect due to the electronegative oxygen, followed by an aromatic ring, followed by alkenes and finally terminal alkynes. (ne sp -) alkene - aromatic ppm 5.7 ppm simple vinylic protons aldehyde ppm simple aromatic protons 9-0 ppm aldehydes ppm vinylic protons (resonance and inductive withdrawal) alkyne ppm aromatic protons (resonance and inductive withdrawal) ppm terminal alkyne protons ppm ppm ppm vinylic protons (resonance donation and inductive withdrawal) ppm ppm aromatic protons (resonance donation and inductive withdrawal) 4. There are several kinds of hydrogen attached to heteroatoms. Some of these are listed below. ften these hydrogens do not follow the + rule because they exchange via acid/base proton exchanges and are not next to neighbor protons long enough to allow coupling to be observed. They are often observed as broad singlets (sometimes so broad they are not easily seen in the spectra). If the exchange rate is very fast among the exchangeable protons on the M time scale, all of the exchangeable protons may appear together at a single, averaged chemical shift. - 5 ppm alcohols 7-5 ppm phenol and enol protons - 2 ppm amines 0-2 ppm carboxylic acids - 6 ppm amides Z:\classes\spectroscopy\all spectra tables for web.d

12 Beauchamp Spectroscopy Tables 2 When carbons are decoupled from their attached hydrogens they all appear as singlets (as if there were no hydrogen neighbors). When carbons are coupled to their hydrogens, carbons follow the + rule. Methyls appear as quartets = q, methylenes appear as triplets = t, methines appear as doublets = d, and carbons without hydrogen appear as singlets = s. arbon chemical shifts are spread out over a larger range than proton chemical shifts (they are more dispersed). It is less likely that two different carbon shifts will fall on top of one another. owever, the relative positions of various types of proton and carbon shifts have many parallel trends (shielded protons tend to be on shielded carbons, etc.) Simple alkane carbons ppm ppm ppm ppm (q) (t) (d) (s) sp 3 carbon next to oxygen ppm ppm ppm (q) (t) (d) ppm (s) sp 3 carbon next to nitrogen ppm ppm ppm (q) (t) (d) ppm (s) sp 3 carbon next to bromine or chlorine ppm (t) ppm (d) ppm (s) sp carbon (alkynes) sp carbon (nitriles) ppm 0-25 ppm sp 2 carbon (alkenes and aromatics) ppm ppm simple sp 2 carbon resonance donation moves lower, resonance withdrawal moves higher sp 2 carbon attached to an electronegative atom ( = oxygen, nitrogen, halogen) or β carbon conjugated with a carbonyl group ppm carboxyl carbons (acids, esters, amides) (s) ppm aldehyde carbons, lower values when conjugated (d) ppm ketone carbons, lower values when conjugated (s) Z:\classes\spectroscopy\all spectra tables for web.d

13 Beauchamp Spectroscopy Tables 3. ne nearest neighbor proton observed proton B o a one neighbor proton = a E to flip proton Protons in this environment have a small cancellation of the external magnetic field, B o, and produce a smaller energy transition by that tiny amount. E (observed) perturbation(s) by neighbor proton(s) increasing increasing E (ν, B o ) E 2 (observed) the ratio of these two populations is about 50/50 (or :) J a Protons in this environment have a small additional increment added to the external magnetic field, B o, and produce a higher energy transition by that tiny amount. J = coupling constant small difference in energy due to differing neighbor's spin (in z) J (z) + rule ( = # neighbors) # peaks = + = + = 2 peaks 2. Two nearest neighbor protons (both on same carbon or one each on separate carbons) observed proton a two neighbor protons b E to flip proton E (ppm) the ratio of these four populations is about :2: E 2 E 3 J a B o two neighbor protons are like two small magnets that can be arranged four possible ways (similar to flipping a coin twice) two equal energy populations here J (z) J (z) J b 2 J b + rule ( = # neighbors) # peaks = + = 2 + = 3 peaks (ppm) 3. Three nearest neighbor protons (on same carbon, or two on one and one on another, or one each on separate carbons) observed proton a c three neighbor protons b E to flip proton E the ratio of these eight populations is about :3:3: E 2 E 3 J a B o E 4 J b J b three neighbor protons are like three small magnets that can be arranged eight possible ways (similar to flipping a coin thrice) three equal energy populations at each of middle transitions J c J c J c 3 3 J (z) J (z) J (z) + rule ( = # neighbors) # peaks = + = 3 + = 4 peaks (ppm) Z:\classes\spectroscopy\all spectra tables for web.d

14 Beauchamp Spectroscopy Tables 4 Multiplets when the + rule works (all J values are equal). s = singlet d = doublet t = triplet q = quartet qnt = quintet sex = sextet sep = septet o = octet peak = 00% peak = 50% peak = 25% peak = 2% peak = 6% peak = 3% peak =.5% peak = 0.8% relative sizes of peaks in multiplets ombinations or these are possible. dd = doublet of doublets ddd = doublet of doublet of doublets dddd = doublet of doublet of doublet of doublets dt = doublet of triplets td = triplet of doublets etc. Z:\classes\spectroscopy\all spectra tables for web.d

15 Beauchamp Spectroscopy Tables 5 oupling onstants ange ange 0-30 z 4 z b geminal protons - can have different chemical shifts and split one another if they are diastereotopic ange a a b 6-8 z 7 z a b cis / allylic coupling, notice through 4 bonds a 0-3 z z ange b 0-3 z z vicinal protons are on adjacent atoms, when freely rotating coupling averages out to about 7 z a b θ = dihedral angle ange 0-2 z 7 z depends on dihedral angle, see plot of Karplus equation trans / allylic coupling, notice through 4 bonds a b sp 2 vicinal coupling (different π bonds) ange 9-3 z 0 z ange ange a b 0- z 0 z protons rarely couple through 4 chemical bonds unless in a special, rigid shapes (i.e. W coupling) ange a b sp 3 vicinal aldehyde coupling -3 z 2 z ange a b 0-3 z 2 z a b 5-8 z 6 z sp 2 geminal coupling sp 2 vicinal aldehyde coupling ange ange a b 5- z 0 z b a 2-3 z 2 z sp 2 cis (acylic) coupling (always smaller than the trans isomer) sp / propargylic coupling notice through 4 bonds a b ange -9 z 7 z a b ange 2-3 z 3 z sp 2 trans coupling (always larger than the cis isomer) a b Z:\classes\spectroscopy\all spectra tables for web.d bis-propargylic coupling notice through 5 bonds ange ortho, meta and ange para coupling to ortho 4-0 z 7 z this proton ortho 6-0 z 9 z meta 2-3 z 2 z para 0- z 0 z sp 2 / sp 3 vicinal coupling para When J values are less than z, it is often difficult to resolve them and a peak may merely appear wider and shorter. meta