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Glossary of WF IR

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Raman vs IR
Vibrations symmetrical about the centre of symmetry are active in the Raman and inactive in the infrared (fig. 2.12); those vibrations which are not centrosymmetric are inactive in the Raman and usually active in the infrared.
Bending vibrations usually lay where?
below the fingerprint area, but exception is N-H bending which appears 1600-1500.
Absorption frequencies of single bonds to hydrogen lay where?
3600-2000
SP3 C-H stretch and bending
Stretch: 3000-2800, Bending: fingerprint
SP2 C-H streching
just above 3000
Terminal acetylene streching
Terminal acetylene streching: strong, sharp line close to 3300.
Aldehyde C-H streching
Aldehyde C-H streching: 2760
C-H from ethers and amines streching
C-H from ethers and amines streching: shows bands in low-frequency region 2850-2750.
Out-of-plane vibrations of trans -CH=CH- double bonds
Out-of-plane vibrations of trans -CH=CH- double bonds: narrow range 970-960 or slightly higher frequency if conjugated, AND always strong.
Out-of-plane vibrations of cis -CH=CH- double bonds? (compared to trans)
Out-of-plane vibrations of cis -CH=CH- double bonds (compared to trans): lower intensity, lower frequency; typically in 730-675 range
O-H bonds not involved in hydrogen bonding? (vapour phase, very dilute solutions or steric hindrance)
O-H bonds not involved in hydrogen bonding (vapour phase, very dilute solutions or steric hindrance): sharp band in 3650-3590 range
O-H alcohol in pure liquieds, solids and many solutions?
O-H alcohol in pure liquieds, solids and many solutions: broad strong band in the 3600-3500 range.
Carboxylic acid absorption?
Carboxylic acid: broad absorption 3200-2500 range AND 1710-1650 region.
Carboxylic acid (IN SOLID PHASE):
Carboxylic acid (IN SOLID PHASE): only shows strong broad band in 3400-2500 range.
Thiol S-H stretching?
Thiol S-H stretching: weak and slightly broadened band near 2600.
Amine N-H stretching?
Amine N-H stretching: 3500-3300.

Because and N-H has a weaker tendency to form a hydrogen bond, its absorption is often sharper than alcohol.

primary amines and amindes stretching vibrations?
primary amines and amindes: give rize to two bands, typically at 3500 and 3400 due to symmetrical and unsymmetrical streching.
Secondary amines stretching vibrations?
Secondary amines stretching vibrations: only one band observed, BUT

s-cis configuration show several bands from various hydrogenbonded associations (solid state). see 36.

Amine salts and zwitterions of amino acids N-H streching:
Amine salts and zwitterions of amino acids N-H streching: several bands on the low-frequency side of any C-H absorption, sometimes as low as 2000.
primary and secondary amides N-H bending vibrations?
primary and secondary amides N-H bending vibrations: just above the fingerprint area called amide-II band (see carbonyl group section)
absorption frequencies of triple and cumulated double bonds?
absorption frequencies of triple and cumulated double bonds: 2300-1930
absorption internal acetylenes?
absorption internal acetylenes: 2270-2150 range
absorption conjugated tripple bonds and enynes?
absorption conjugated tripple bonds and enynes: lower end of 2260-2150cm
Nitrile absorb where and intensity?
Nitrile absorb at 2260-2200cm, but are often weak
Conjugation does what to the frequency?
Conjugation LOWERS the frequency by approx. 25cm meaning the binding strength is lowered.
Stretching vibration of two double bonds in cumulated double-bonded systems X=Y=Z with an unsymmetrical and a symmetrical pair. Absorption region and strength?
Stretching vibration of two double bonds in cumulated double-bonded systems X=Y=Z with an unsymmetrical and a symmetrical pair. Absorption region and strength?

The former strong band at 2350-1930cm and latter band in fingerprint region.

CO2 absorps where?
CO2 absorps at 2349cm
Allenes C=C=C absorb where?
Allenes C=C=C absorb sharply at 1950-1930cm
Absorption frequencies of the double-bond region is where?
Absorption frequencies of the double-bond region is at 1900-1500cm
C=O double bonds. how do

ester
ketone
acids
aldehydes
amide

corrospond to each other in intensity?







C=O double bonds.

acid >= ester > ketone = aldehyde = amide

ester sometime stronger than acid,
amide subject to greater variations compared to ketone




The rule about electronegative elements besides carbonyls?
The more electronegative the group X in the system R-C(=O)-X, the higher is the frequency, except that this trend from the inductive effect of X is offset by the effect in the pi-system of any lone pairs on X.
Anhydride > acid chlorides > esters > aldehydes > ketones > acids > amides > acylsilanes > carboxylate ions

What are the frequencies?

Anhydride 1820 & 1760 > acid chlorides 1800 > esters 1740 > aldehydes 1730 > ketones 1710 > acids 1710 > amides 1660 > acylsilanes 1640 > carboxylate ions 1580

p.38

The extra point about the effect on X in R-C(=O)-X?
The extra point about the effect on C-X in R-C(=O)-X is that while C=O is weakened by electronegative X, the C-X is increased in frequency.
The rule about hydrogen bonding and carbonyl groups
Hydrogen bonding to a carbonyl group causes a shift to lower frequency of 40-60cm. Acids, amides with an N-H, enolised beta-dicarbonyl systems, and a o-hydroxy- and o-aminophenyl carbonyl compounds show this effect

p. 38

The rule about carbonyl compounds in solid state compared to dilute solutions

All carbonyl compounds tend to give slithly lower values for the carbonyl stretching frequency in the solid state compared with the value for dilute solutions.

p. 38

The rule about alpha-beta-unsaturation and carbonyl groups
alpha-beta-unsaturation causes a lowering of frequency of 15-40cm because overlap similar to that illustrated for the amide in fig. 2.9 but less effective, reduces the double-bond character of the C=O bond.

p. 38

The effect of alpha-beta-unsaturation for amides
The effect of alpha-beta-unsaturation is noticeably less in amides, where little shift is observed, and that sometimes even to higher frequency.

p.38

The rule about ring strain in cyclic compouns and carbonyls
Ring strain in cyclic compounds causes a relatively large shift to higher frequency (fig. 2.10). For ketone and ring system
C3 = 1813
C4 = 1775
C5 = 1750
C6 = 1715
C7 = 1710

Also apply for esters and amides (different numbers, but same tendency)

p.39








Differents effects on carbonyl frequency are all ......
Differents effects on carbonyl frequency are all ADDITIVE!

p39

Special about primary and secondary amides in the lower region?



Primary and secondary amides show at least two bands, e.i. the Amid II and Amid I band.
Amid II and Amid I bands frequency?
Amid I band 1660cm
The higher frequency is more or less the localised stretching vibration of the C=O group

Amid II band 1560cm
Kiwer frequency is the more or less localised bending vibration of the N-H bond.

p39





C=N double bonds absorption?
C=N absorp at 1690-1630cm. Weaker than carbonyl and absorp in same region as C=C.
C=C double bonds (table 2.10) absorption?

what about degree of substitution?

C=C double bonds (table 2.10) absorb at 1680-1620cm.

The heavier substituted C=C absorb at high-frequency end and the less substituted at the low-frequency end.

What about symmetrical substitution of e.g. C=C or triple CC?
Symmetrical substitution of e.g. C=C or triple CC are absent because of symmetrical vibration. USE RAMAN!

p 40

The rule about C=C Double bond exocyclic and the ring size?
C=C Double bond exocyclic to a ring the frequency rises as the ring size decrease

p40

The rule about double bond within a ring and the ring-size
A double bond within a ring: the frequency falls as the size decreases

OR

=C-H stretching frequency rises slightly as ring strain increases, and the =C-H vibration frequencies may give additional structural information (cis/trans)

p40





Aromatic rings absorb at ??? with two bonds
Aromatic rings absorb at 1600-1500cm with two bonds.

If aromat is conjugated to double bond, three bonds are usually present.

p40



Aromatic has weak C-H stretching band near ?????
Aromatic has weak C-H stretching band near 3030cm

p40

Aromatic combination of overtones (2-6 bands) in the 2000-1600 region is usefull how?
Aromatic combination of overtones (2-6 bands) in the 2000-1600 region is usefull for nothing. We use HNMR now.

p41

N=O double bonds like nitro has unsymmetrical and symmetrical N=O stretching vibrations.

Latter and former frequency and intensity?

N=O double bonds like nitro has strong unsymmetrical band in 1570-1540cm and a strong symmetrical band in 1390-1340cm

p41

Nitrates, nitramines, nitriles and nitroso compounds also absorb in the ???? region
Nitrates, nitramines, nitriles and nitroso compounds also absorb in the 1650-1400 region

p41

Groups absorbing in the finger print region?
absence can be usefull?

p41

table 2.1 C-H stretching vibration:

C(triple)C-H

table 2.1 C-H stretching vibration:

C(triple)C-H ~3300cm Sharp

table 2.1 C-H stretching vibration:

C=CH2
C=C-H
aryl-H



table 2.1 C-H stretching vibration:

C=CH2 3095-3075(m)
C=C-H 3040-3010(m)
aryl-H 3040-4010(w)



table 2.1 C-H stretching vibration:

cyclopropane C-H
Epoxide C-H
-CH2-halogen
-COCH3




table 2.1 C-H stretching vibration:

cyclopropane C-H ~3050(w)
Epoxide C-H ~3050(w)
-CH2-halogen 3100-2900(w)
-COCH3 3100-2900(w)




table 2.1 C-H stretching vibration:

unfunctionalised C-H
--CH2 and -CH3
---CH



table 2.1 C-H stretching vibration:

unfunct. C-H 2960-2850(s)
--CH2 and -CH3 2960-2850(s)
---CH 2890-2880(w)



table 2.1 C-H stretching vibration:

-CHO

table 2.1 C-H stretching vibration:

-CHO 2900-2700(w)
Usually two bands, one near 2720cm


table 2.1 C-H stretching vibration:

-OCH3

table 2.1 C-H stretching vibration:

-OCH3 2850-2810(m)

table 2.1 C-H stretching vibration:

--NCH3 and --NC(-)H2

table 2.1 C-H stretching vibration:

--NCH3 and --NC(-)H2
2820-2780(m)


table 2.1 C-H stretching vibration:

-OCH2O-

table 2.1 C-H stretching vibration:

-OCH2O- 2790-2770(m)

table 2.2 C-H bending vibration:

--CH2 and -CH3

table 2.2 C-H bending vibration:

--CH2 and -CH3
1470-1430(m) asymetrical deformations


table 2.2 C-H bending vibration:

-C(CH3)3

table 2.2 C-H bending vibration:

-C(CH3)3
1395-1385(m) and 1365(s)


table 2.2 C-H bending vibration:

-CH3
symmetrical deformations


table 2.2 C-H bending vibration:

-CH3 1390-1370(m) symmetrical deformations

table 2.2 C-H bending vibration:

-OCOCH
The high intensity of these bands often dominates this region of the spectrum


table 2.2 C-H bending vibration:

-OCOCH 1385-1365(s)
The high intensity of these bands often dominates this region of the spectrum


table 2.2 C-H bending vibration:

--C(CH3)2
A roughly symmetrical doublet


table 2.2 C-H bending vibration:

--C(CH3)2 ~1380(m)
A roughly symmetrical doublet


table 2.2 C-H bending vibration:

-COCH3

table 2.2 C-H bending vibration:

-COCH3 1360-1355(s)

table 2.2 C-H bending vibration:

-CH=CH2

table 2.2 C-H bending vibration:

-CH=CH2
995-985(s) and 940-900(s)


table 2.2 C-H bending vibration:

-CH=CH- (trans)

C-H out-of-plane deformation. Conjugation shifts the band towards 990cm



table 2.2 C-H bending vibration:

-CH=CH- (trans) 970-960(s)

C-H out-of-plane deformation. Conjugation shifts the band towards 990cm



table 2.2 C-H bending vibration:

--C=CH-

table 2.2 C-H bending vibration:

--C=CH- 840-790(m)

table 2.2 C-H bending vibration:

--C=CH2

table 2.2 C-H bending vibration:

--C=CH2 895-885(s)

table 2.2 C-H bending vibration:

-CH=CH-

C-H out of plane deformation



table 2.2 C-H bending vibration:

-CH=CH- 730-675(m)

C-H out of plane deformation



table 2.2 C-H bending vibration:

--CH2

Rocking



table 2.2 C-H bending vibration:

--CH2 ~720(w)

Rocking



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