Spectra: Mass, IR, UV Vis

Question 1

How is a fragment created?

Answer 1

• A high energy beam knocks out a non-bonding electron creating a detectable cation and a non-detectable radical
• Exactly 1 covalent bond is broken in each molecule. (Thousands of molecules lead to many bond breaking possibilities)

Question 2

How are molecule fragments detected?

Answer 2

They must have a charge. Usually of +1
Neutral fragments with radicals undetected

Question 3

Cl Mass Spec

Answer 3

35Cl and 37 Cl = 3:1 ratio

Question 4

Br Mass Spec

Answer 4

79Br and 81Br = 1:1 ratio

Question 5

How does the number of carbons in a molecule affect the M+1 peak due to C13?

Answer 5

C13 has a 1.1% abundance. For each carbon in a molecule multiply the number by 1% and that is how much the peak abundance will multiply by.

Ex. C10H22 10 C x 1% = 10% C13 peak abundance increase

Question 6

Base Peak

Answer 6

Fragment at 100% intensity -tallest peak

Question 7

Mass Spec Vertical Axis

Answer 7

Shows abundance of fragments

• taller peak = more abundance (more stable, many identical Carbon configurations)

Question 8

Parent Peak

Answer 8

unfragmented cation peak (original molecule)

Question 9

Mass Spectrometry

Answer 9

Measures mass or molecular weight of molecule and fragments

Question 10

IR Spectrometry

Answer 10

Infrared wavelengths detected to determine functional groups

Question 11

Overtone Bands

Answer 11

Aromatics: 4-6 Small bumps at 2000-1650 cm-1

Question 12

C=O

Answer 12

Carbonyl: Sharp peak at 1700 cm-1
(2000-1500)

Question 13

Saturated Bonds

Answer 13

Sp3 C-H Stretch: Peak around 3000-2850 cm-1
- Carbons have max number of Hydrogens

Question 14

Unsaturated Bonds

Answer 14

Sp2 C-H Stretch: Peak around 3100-3000 cm-1

• Carbons have double/triple bonds for fewer Hydrogens)

Question 15

C-O Stretch

Answer 15

Ethers, Alcohols, Carboxylic Acid, Epoxide: Peak around 1260 - 1050 cm-1

Question 16

Aldehyde Peak

Answer 16

Doublet peak at 2830-2700 cm-1
- Can shoulder C-H alkyl peak below 3000 cm-1

Question 17

Aromatic Peak:

Answer 17

Above 3000 cm-1

Question 18

C-OH

Answer 18

Alcohol, Carboxylic Acid, Aldehyde: Broad smooth peak around 3650-3200 cm-1

Question 19

C-N

Answer 19

Amine: Medium peak at 1250-1020 cm-1

Question 20

Energy of a photon is _________ proportional to frequency and _________ proportional to wavelength

Answer 20

Directly, Inversely
E = hf
E = hc/y

Question 21

Functional Group likely to give an odd number m/z?

Answer 21

Amine. Nitrogen with odd mass number (15) gives odd mass

Question 22

M-18 fragmentation caused by…

Answer 22

Alcohol (1* or 2* C) dehydration.

Question 23

Order of ionization preference…

Answer 23

non-bonding e- > pi e- > sigma e-

Question 24

Carboxylic acid (COOH) vs Alcohol

Answer 24

COOH has a broader peak than Alcohol