IR Summary - All numerical values in the tables below are given in wavenumbers, cm -1

Transcription

1 Spectroscopy Data 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:\files\classes\spectroscopy\typical spectra charts.d

2 Spectroscopy Data 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:\files\classes\spectroscopy\typical spectra charts.d

3 Spectroscopy Data 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:\files\classes\spectroscopy\typical spectra charts.d

4 Spectroscopy Data 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:\files\classes\spectroscopy\typical spectra charts.d

5 Spectroscopy Data Tables 5 deshielding side = less electron rich and 3 M chemical shift values. shielding side = more electron rich (inductive & resonance) (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. 5 alcohol amide - 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:\files\classes\spectroscopy\typical spectra charts.d

6 Spectroscopy Data 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) d. methyl c. methyl e. methylene f. methylene a. methine b. methylene Starting value and equations for 3 's δ 3 = α 3 α δ 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 δ 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 δ =.5 + (α +β + γ) 3 is the summation symbol for all substituents considered β α is the summation symbol for all substituents considered γ alculations are generally close to actual chemical shifts for a single substituent, but are less reliable as the number of substituent factors goes up. Multiple substituent factors tend to overestimate an actual chemical shift. β γ γ a. methine =.5 + (.4) α + (2.3) α + (0.2) β = 5.4 ppm actual = 5.2 b. methylene =.2 + (.5) α + (0.4) β + (0.3) β = 3.4 ppm actual = 3.0 and 3.2 c. methyl = (.5) α = 2.4 ppm actual = 2.6 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:\files\classes\spectroscopy\typical spectra charts.d

7 Spectroscopy Data 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 δ(ppm) = α gem + α cis + α trans gem trans cis δ gem = = 6.6 actual = 6.6 b δ trans = = 5. actual = 5. a δ cis = = 5.7 actual = 5.6 c d e f δ a = (-0.4) = 4.8 actual = 4.9 (J = 4,.6 z) δ b = (-0.6) = 4.6 actual = 4.6 (J = 6,.6 z) δ c = = 7.3 actual = 7.4 (J = 4, 6 z) δ d = = 6.0 actual = 6.2 (J = 8, z) δ e = = 5.7 actual = 5.8 (J =,.4 z) δ f = = 6.2 actual = 6.4 (J = 8,.4 z) Z:\files\classes\spectroscopy\typical spectra charts.d

8 Spectroscopy Data Tables 8 Estimated chemical shifts for protons at aromatic sp 2 carbons Substitution relative to calculated "" Substituent α ortho α meta α para meta ortho 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 para meta ortho δ(ppm) = α ortho + α meta + α para Example alculation δ ( 3 ) = = 3.7 actual = δ (2) = (-0.5) ortho + (-0.) para = 6.7 actual = δ (3) = (-0.2) ortho + (-0.4) para = 6.7 actual = δ ( 2 ) =.2 + (0.8)α + (.4)α = 3.4 actual = δ (5) = (0.7) gem = 5.9 actual = δ (6) = (-0.2) trans = 5.0 actual = δ (7) = (-0.2) cis = 5.0 actual = 5. Z:\files\classes\spectroscopy\typical spectra charts.d

9 Spectroscopy Data Tables 9 eal Examples of ombination Effects on hemical Shifts π bond anisotropy 0.8 shielded σ bond example too ( 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 = 3-4 hydrogen bonding 2 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:\files\classes\spectroscopy\typical spectra charts.d

10 Spectroscopy Data Tables 0. ne nearest neighbor proton increasing δ one neighbor proton = increasing E (ν, B o ) a observed proton B o 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) 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 δ (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 δ (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 δ (ppm) Z:\files\classes\spectroscopy\typical spectra charts.d

11 Spectroscopy Data Tables Splitting patterns when the + rule works (common, but not always true) = group without any coupled proton(s) = 0 = = 2 = s, J=none I= =0 d, J=7 I= = t, J=7 I= =2 2 q, J=7 I= =3 δ = calc or exp δ = calc or exp δ = calc or exp δ = calc or exp = = qnt, J=7 I= =4 2 sex, J=7 I= =5 δ = calc or exp δ = calc or exp = 6 = sep, J=7 I= = oct, J=7 I= =7 2 = 8 δ = calc or exp non, J=7 I= =8 δ = calc or exp δ = calc or exp Pascal's triangle = coefficients of variable terms in binomial expansion (x + y) n, n = integer 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% 5 peak =.5% 5 6 peak = 0.8% relative sizes of peaks in multiplets (% edge peak shown) 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:\files\classes\spectroscopy\typical spectra charts.d

12 Spectroscopy Data Tables 2 oupling onstants ange ange a 0-30 z 4 z b geminal protons - can have different chemical shifts and split one another if they are diastereotopic a b ange 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 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 Z:\files\classes\spectroscopy\typical spectra charts.d

13 Spectroscopy Data Tables 3 Similar chemical shift information presented in a different format. emember, proton decoupled carbons appear as singlets. When carbons are coupled to their hydrogens, carbons follow the + rule. Methyls = q, methylenes = t, methines = d, and carbons without hydrogen appear as singlets = s. DEPT provides the same information. arbon chemical shifts are spread out over a larger range than proton chemical shifts (they are more dispersed), so it is less likely that two different carbon shifts will fall on top of one another. 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 d ppm d ppm d ppm d ppm (q) (t) (d) (s) sp 3 carbon next to oxygen d ppm d ppm d ppm (q) (t) (d) d ppm (s) sp 3 carbon next to nitrogen d ppm d ppm d ppm (q) (t) (d) d ppm (s) sp 3 2 carbon next to bromine or chlorine ( = l, Br) d ppm d ppm (t) (d) d ppm (s) sp carbon (alkynes) sp carbon (nitriles) δ ppm δ 0-25 ppm sp 2 carbon (alkenes and aromatics) δ ppm δ ppm simple sp 2 carbon resonance donation moves δ lower, resonance withdrawal moves δ higher sp 2 carbon attached to an electronegative atom ( = oxygen, nitrogen, halogen) or β carbon conjugated with a carbonyl group δ ppm carboxyl carbons (acids, esters, amides) (s) δ ppm aldehyde carbons, lower values when conjugated (d) δ ppm ketone carbons, lower values when conjugated (s) Z:\files\classes\spectroscopy\typical spectra charts.d

14 Spectroscopy Data Tables 4 alculations of alkane 3 chemical shifts not listed above. sp 3 arbon hemical Shift alculations alculations for sp 3 carbon 3 chemical shifts of functionalized carbon skeletons can be performed starting from the actual shifts found in the corresponding alkane skeleton, and introducing corrections factors based on the functionality present in the molecule. This assumes that the alkane 3 shifts are available, which is why several examples are provided below. Examples of n alkanes as possible starting points for calculation 3 shifts in ppm. Steric orrections for sp 3 carbon chemical shift calculations The calculated carbon atom is: primary secondary tertiary quaternary The attached α carbons are: primary secondary tertiary quaternary Approximate 3 shift calculation from scratch. δ = -(2) + 9x(#α + #β) - 2x(#γ ) + steric corrections = (+3) - 2(2) + (-3) = 29 (actual = 28.3) 2 = (4+2) - 2(2) + [3x(-.5)+(-5.0)] = 28 (actual = 34.0) = (3+5) - 0(2) + [(-9.5)+(-5.0)] = 45 (actual = 47.9) 5 4 = (3+2) - 3(2) + (-9.5) = 27 (actual = 27.2) 6 5 = (+2) - 2(2) + (-) = 20 (actual = 9.5) 6 = (+2) - 5(2) + (-) = 4 (actual = 8.5) 3 shifts for various carbon alkane skeletons - useful starting points for calculating sp3 carbon chemical shifts Z:\files\classes\spectroscopy\typical spectra charts.d

15 Spectroscopy Data Tables 5 α γ α γ β β is attached to a terminal carbon atom (ppm) is attached to an internal carbon atom (ppm) Substituent = α correction β correction γ correction α correction β correction γ correction ( 3 ) ( 3 ) is attached to a terminal carbon atom (ppm) is attached to an internal carbon atom (ppm) Substituent = α correction β correction γ correction α correction β correction γ correction ( 3 ) ( 3 ) Z:\files\classes\spectroscopy\typical spectra charts.d

16 Spectroscopy Data Tables 6 is attached to a terminal carbon atom (ppm) is attached to an internal carbon atom (ppm) Substituent = α correction β correction γ correction α correction β correction γ correction F l Br I is attached to a terminal carbon atom (ppm) is attached to an internal carbon atom (ppm) Substituent = α correction β correction γ correction α correction β correction γ correction l S S Z:\files\classes\spectroscopy\typical spectra charts.d

17 Spectroscopy Data Tables 7 Additional starting point for calculating 3 chemical shifts (ppm) of substituted benzene rings (just a few possibilities) 28 ppm starting point for benzene carbon Substituent Use correction term for carbon atom in relative position to the substituent. Start with 28 ppm. Starting points for other common ring systems. (ppm). o correction terms included for substituents Substituent Z Z 2 Z 3 Z ( 3 ) ( 3 ) F l Br I S = F l Br I Substituent Z Z 2 Z 3 Z = S S S() S S 2 l l Li MgBr naphathalene 36 S pyridine pyrrole furan thiophene Additional starting point for calculating 3 chemical shifts (ppm) of substituted alkenes (just a few possibilities) 23 ppm starting point for alkene carbon γ β α α ' β ' γ ' 23 + correction factors increments for directly attached carbon atoms α = β = 5 γ = -2 α ' = -8 β ' = -2 γ ' = 2 steric corrections for each pair of cis-α,α ' substituents - for each pair of geminal-α,α substituents -5 for each pair of geminal-α,α 'substituents 3 if one or more β sutstituents are present 2 Z 2 Effect of substituents on alkene 3 shifts (ppm) δ = 23 ppm + Z i Substituent Z Z ( 3 ) ( 3 ) l Br -5-2 I = Substituent Z Z 2 -F l 3-6 -Br I ( 3 ) S l 8 4 Z:\files\classes\spectroscopy\typical spectra charts.d

18 Spectroscopy Data Tables 8 ommon fragmentation patterns in mass spectroscopy. Branch next to a π bond radical cation π bond of an alkene or an aromatic Pi electrons partially fill in loss of electrons at carbocation site via resonance. This is common fragmentation for alkenes and aromatics haracteristic carboncation stability also applies. 3 o > 2 o > o > 3 2. Branch next to an atom with a lone pair of electrons radical cation lone pair electrons partially fill in loss of electrons at carbocation site via resonance. This is a common fragmentation for any atom that has a lone pair of electrons (oxygen = alcohol, ether, ester; nitrogen = amine, amide, sulfur = thiol or sulfide, etc.). Alcohols often lose water (M-8) and primary amines can lose ammonia (M-7). 3. Branch next to a carbonyl (=) bond and possible subsequent loss of carbon monoxide, 2 radical cation or 2 can be lost from aldehydes, ketones, acids, esters, amides...etc. 2 An oxygen lone pair partially fill in the loss of electrons at the carbocation site via resonance. This is a common fragmentation pattern for any carbonyl compound and can occur from either side, though some are more common than others. 2 loss of 2 subsequent loss of is possible after α fragmentation so not only can you see loss of an α branch you can see the mass of an α branch. 4. McLafferty earrangement γ α β radical cation cation This is another common fragmentation pattern for carbonyl compounds (and other pi systems as well: alkenes, aromatics, alkynes, nitriles, etc.). If the pi bond has at least 3 additional nonhydrogen atoms attached and a hydrogen on the "gama" atom, the branch can curve around to a comfortable 6 atom arrangement and the pi bond can pick up a hydrogen atom and cut off a fragment between the α and β positions. The positive charge can be seen on either fragment and usually the fragments have an even mass (unless there is an odd number of nitrogen atoms). α still a radical γ β lost neutral fragment Positive charge can beon either fragment, which typically have an even mass. α = alpha position β = beta position γ = gama position Knowing these few fragmentation patterns will allow you to make many useful predictions and interpretations. Loss of small molecules, via elimination is common: 2 = 8, 2 S = 34, 3 = 32, 2 5 = 46, 3 = 7, 3 2 = 62, F = 20, l = 36/38, Br = 80/82, etc. Z:\files\classes\spectroscopy\typical spectra charts.d

19 Spectroscopy Data Tables 9 A sampling of unusual and/or miscellaneous peaks that are commonly seen, (even when they don't make sense). 3 = = = = 57 5 = = 85 mass = 39 ( = ) 53 ( = 3 ) 67 (= 2 3 ) also works for 2 mass = 4 ( = ) 55 ( = 3 ) 69 (= 2 3 ) mass = 65 ( = ) 79 ( = 3 ) 93 (= 2 3 ) mass = 9 ( = ) 05 ( = 3 ) 9 (= 2 3 ) mass = 27 2 mass = 44 Loss of small molecules via elimination reactions. 2 2 S F l Br mass = McLafferty Possibilities 2 otice! McLafferty 2 even masses 2 2 mass = 44 ( = ) 58 ( = 3 ) 72 (= 2 3 ) 86 ( = 3 7 ) Similar Patterns mass = 77 mass = 45 ( = ) 59 ( = 3 ) 73 (= 2 3 ) 2 mass = 42 ( = ) 56 ( = 3 ) 70 (= 2 3 ) variable mass, (can sometimes see cation on this side too) = mass = 29 ( = ) 43 ( = 3 ) 57 (= 2 3 ) 7 ( = 3 7 ) 05 ( = 6 5 ) 2 mass = 28 ( = ) 42 ( = 3 ) 56 (= 2 3 ) 70 ( = 3 7 ) mass = 42 ( = ) 56 ( = 3 ) 70 (= 2 3 ) 84 ( = 3 7 ) mass = 92 ( = ) 06 ( = 3 ) 20 (= 2 3 ) 34 ( = 3 7 ) mass = 40 ( = ) 54 ( = 3 ) 68 (= 2 3 ) 82 ( = 3 7 ) mass = 4 ( = ) 55 ( = 3 ) 69 (= 2 3 ) 83 ( = 3 7 ) Z:\files\classes\spectroscopy\typical spectra charts.d