Question

Can someone please provide me the easiest way to memorize IR spectra values above the fingerprint region. Just some simple hints or good ways to look at compounds to graphs would be great! I also need some help with remembering CNMR spectra too. Any help is greatly appreciated.

Answer 1

Solution:

The easiest way to memorize IR spectra values above the fingerprint region. Just some si

S.No(For hydrocarbons)	Bond/Compound type	Frequencies(in cm-1)
1	C-H (Alkynes)	3300
2	C-H aromatic rings	3000-3100m, 675-870
3	C-H (Alkenes)	3020-3080m,675-1000
4	C-H (Alkanes)	2850-2960,1350-1470
5	C≡C alkynes	2100-2260v
6	C=C alkenes	1640-1680v
7	C≈C aromatic rings	1500,1600v
S.No(For carbonyl compounds)
1	O-H (monomeric alcohols and phenols	3610-3640v
2	O-H (hydrogen bonded alcohols and phenols)	3200-3600 broad
3	O-H in carboxylic acids	2500-3000 broad
4	C=O(aldehydes, ketones, carboxylic acid and esters)	1590-1760
5	C-O (alcohols, ethers, esters and carboxylic acids	1080-1300
For compounds containing N
1	N-H amines	3300-3500m
2	C≡C nitriles	2210-2260v
3	C-N amines	1180-1360
4	-NO2 nitro compounds	1515-1560,1345-1385

[Note: m for moderate, v for variable and ≈ for mix of single and double bonds.]

Hints: i) remember from highest frequency value to lowest. ii)Frequency for C-H bond is alkyne> aromatic rings> alkenes > alkanes. iii)Frequency for ‘C’ and ‘C’ is alkyne> alkenes > aromatic rings.

C13 NMR

Carbon environment	Chemical shift ppm
C-C	0-50
C- O	50-100
C= C	100-150
This short form can be elaborated as follows
C=O(ketones)	205-220
C=O(aldehydes)	190-200
C=O (in acids and esters)	160-185
C(in aromatic rings)	125-150
C=C(in alkenes)	115-140
RCH2O-	50-90
RCH2Cl	30-60
RCH2NH2	30-65
R3CH	25-35
CH3CO-	20-50
R2CH2	16-25
RCH3	10-15