8. Spectrum continued

Transcription

1 I. The ν(x-h) region alcohols H-bonding in alcohols Figs. 2.30,2.32,2.59,2.61,2.45 w ν(o-h) amines s neat carboxylic acids increasing dilution 3600 free ν(o-h) w HN(C 4 H 9 ) 2 -NHbroad m-s ν(n-h) remember: s and as for -NH ν(o-h) -COOH

2 I. The ν(x-h) region alkynes aromatics Figs. 2.14,2.23,2.10,2.7,2.36 s m-w 3300 ν(c-h) sp > 3000 ν(c-h) sp 2 alkenes alkanes aldehydes m-w s m two bands CH 3 (CH 2 ) 7 O H > 3000 ν(c-h) sp 2 < 3000 ν(c-h) sp ν(c-h) sp 2 -CHO

3 II. The ν(x X) region nitriles alkynes Figs. 2.62,2.14,2.15 w m ν(c N) ν(c C) but compare the symmetric alkyne the same would be true for CH 3 -C C-CH 2 CH 2 CH 3 pseudo-symmetric

4 III. The ν(c=o) region: cm -1 Figs. 2.36,2.45,2.54 aldehyde ketone s carboxylic acid amide further assignment through the exact position in the cm -1 window: Fig. 2.35

5 IV. The ν(c=c) region alkenes aromatics Figs. 2.12,2.25,2.13 (2.13 shows a wrong spectrum in the 5 th edition) m m m-s two bands ν(c=c) 1600 and 1475 ν(c=c) aromatic but compare the pseudo-symmetric alkene ν(c=c) this is getting close to the fingerprint region: this is where our stretch analyses stop, even though some occur at smaller ν ester ν(c-o)???

6 V. Substitution patterns on an aromatic ring overtone and combination Figs. 2.23,2.24,2.26 δ(c-h) oop ar Fig ortho subst. oop give one of these labels as a qualifier on δ(c-h) oop ar

7 V. Substitution patterns on an aromatic ring how to refine information gained upon ν(c-h) sp 2 for an aromatic system ν(c-h) sp 2 overtones aromatic mono-subst. Fig ν(c=c) ar δ(c-h) oop aromatic mono-subst. - check around 3000 cm -1 : > 3000 ν(c-h) sp 2 - check the ν(c=c) region: pattern suggests ν(c=c) ar - check between 2000 and 1670 cm -1 : overtones are present, pattern suggests aromatic mono-substitution - check in the fingerprint between 900 and 690 cm -1 : two bands present, δ(c-h) oop, pattern suggests aromatic mono-substitution

8 VI. Substitution patterns on an alkene C=C δ(c-h) oop alkene Figs. 2.10,2.12,2.13 (2.13 shows a wrong spectrum in the 5 th edition) Fig give one of these labels as a qualifier on δ(c-h) oop alkene

9 VII. Deformation bands from CH 2 and CH 3 groups Figs. 2.7,2.9 δ(ch 3 ) patterns for iso-propyl tert-butyl > 1400 δ(ch 2 ) < 1400 δ(ch 3 ) scissoring 720 cm -1 δ(ch 2 ) rocking Fig δ(ch 2 ) wagging, twisting w, don t need to identify

10 VIII. More overtones Figs. 2.55,2.10 very common: 3600 = overtone, not ν(n-h)! 1800 ν(c=o) also common: 1820 = overtone, not ν(c=o)! 910 δ(c-h) oop alkene

11 IX. Various additional information Figs. 2.56,2.68 > 3000 ν(c-h) sp 2 w, but important need to identify 1740 = overtone, and ν(c=o) at 1740: Fermi-resonance band, not a second ν(c=o)! 870, s 2550 ν(s-h) not ν(c C) or ν(c N)

12 Example A detailed analysis of an IR spectrum without any further information. Fig. 2.39

13 Example A detailed analysis of an IR spectrum without any further information. features ν(c-h) sp 2 ν(c-h) sp 3 ν(c=o) ν(c=c) δ(ch 3 ) =CMe 2 δ(c-h) oop alkene tri-subst. O conjugation CH 3 CH 3 conjugation - definitely: < 3000 ν(c-h) sp 3 - nothing directly > 1400, no δ(ch 2 ) - < 1400 δ(ch 3 ), maybe some i-pr or t-bu-like pattern (p. 38) - probably: > 3000 ν(c-h) sp 2 aromatic or alkene O - but: - below 2000 no aromatic overtones (p. 46) - around 1500 not the typical set of ν(c=c) ar (p. 43) not s δ(c-h) oop aromatic para-subst. (p. 46) probably not aromatic - > 1600 no typical ν(c=c) alkene (p. 34), but lowered to 1620? m δ(c-h) oop alkene tri-subst. (p. 42) probably alkene, but not typical overtone of ν(c=o) at 3380/2 = 1690 very low, in amide region or again not typical - ν(c=o) not aldehyde, not acid, not ester, not amide probably ketone (not typical ) - lowered ν(c=c) alkene and lowered ν(c=o) ketone point to conjugation

14 Example continued A detailed analysis of an IR spectrum with further information. ν(c-h) sp 2 ν(c-h) sp 3 ν(c=o) ν(c=c) δ(ch 3 ) =CMe 2 δ(c-h) oop alkene tri-subst. conjugation - elemental analysis gives C 6 H 10 O - U = ½(10 0) = 7 5 = 2 - possibly C=O and C=C alkene or ring - check for alkene substitution pattern: 5 C taken care of - check for aldehyde or ketone: 6 th C taken care of, plus O, plus all H - notice the possible conjugation, check whether those bands fit - notice the absence of CH 2, check whether those bands are absent - check whether everything makes sense (small ν(c-h) sp 2 ) - put all appropriate labels O O