Spectroscopy measurements

Question 1

what is the IR frequency of bending vibrations for free O-H?

Answer 1

1630 cm^-1

Question 2

what is the IR frequency of stretching vibrations for free O-H?

Answer 2

3700-3600 cm^-1

Question 3

what is the IR frequency of C-H symmetric and asymmetric stretching?

Answer 3

2960-2800 cm^-1

Question 4

what is the IR frequency of saturated C-H stretching?

Answer 4

3000-2900 cm^-1

Question 5

what is the IR frequency of C-H bending vibrations?

Answer 5

1455-1380 cm^-1

Question 6

what is the IR frequency of unsaturated C-H vibrations?

Answer 6

3050-3020 cm^-1

Question 7

what is the IR frequency of alkynes?

Answer 7

3310 cm^-1

Question 8

what is the IR frequency of hydrogen-bonded O-H?

Answer 8

3500-2500 cm^-1

broad peak

Question 9

what is the IR frequency of N-H stretching?

Answer 9

3500-3300 cm^-1

less affected by hydrogen bonding than O-H

Question 10

what is the IR frequency of C=O stretching?

Answer 10

1800-1600 cm^-1

also C=N and C=C at this frequency, but these are not as common

Question 11

what is the IR frequency of N-H bending?

Answer 11

1570 cm^-1
amide II band
sharper than O-H stretching and at a lower frequency

Question 12

what are the three peaks characteristic of a peptide?

Answer 12

amide I 1650 cm^-1
amide II 1570 cm^-1
amide III 1250 cm^-1

Question 13

what is the IR frequency of C≡N?

Answer 13

2300-2100 cm^-1

Question 14

what is the shielding and chemical shift of protons attached to C atoms in CH2 and CH3 groups?

Answer 14

highly shielded

δ~1-4 ppm

Question 15

what is the shielding and chemical shift of protons attached to O?

Answer 15

less shielded

δ~2-5 ppm

Question 16

what is the shielding and chemical shift of protons attached to N?

Answer 16

similar range to O-H

peak often broadened

Question 17

why is the peak for N often broadened?

Answer 17

due to magnetic interactions with N nuclear spins and because of proton exchange

Question 18

what is the shielding and chemical shift of protons in aldehydes and carboxylic acids?

Answer 18

protons are highly deshielded

δ~9-10 ppm

Question 19

explain the chemical shifts of aromatic systems

Answer 19

• electrons travelling around the ring (π orbitals) generate a ring current that adds to B0
  δ~8-9 ppm

Question 20

what is the chemical shift for CH3?

Answer 20

0.9 ppm

Question 21

what is the chemical shift for C6H5-CH3?

Answer 21

2.1 ppm

Question 22

what is the chemical shift for Ar-OH?

Answer 22

4-7 ppm

Question 23

what is the chemical shift for R-COOH?

Answer 23

10-12 ppm