1. Mass Spectrometry

O

10287595729

OO

O

O

DCBA

154 139 125111strongest weakest

1. Mass Spectrometry (cont’d)

C 6 x 12.0000H 13 x 1.0078F 1 x 18.9984O 1 x 15.9949 120.0950

C 5 x 12.0000H 12 x 1.0078O 3 x 15.9949 120.0780

C 9 x 12.0000H 12 x 1.0078 120.0940

C 8 x 12.0000H 8 x 1.0078O 1 x 15.9949 120.0570

O O OF OH

O

C6H13FO C5H12O3 C9H12 C8H8O

1. Mass Spectrometry (cont’d) 2

0 10 20 30 40 50 60 70 80 90 100

88

73

70

45

88 = Molecular ion73 = M+ -15 (loss of methyl)70 = M+ -18 (loss of water)45 = M+ -43 (loss of propyl)

Loss of water indicates the compound is an alcohol. Alcohols also undergo α-cleavage. Alcohol that can lose methyl and propyl via α -cleavage:

OH OH

or

2. Infrared Spectroscopya. Which signal would be more intense in an IR spectrum, a C-O stretch or a C-N stretch? Why?

Intensity of absorption is correlated to change in dipole moment with the vibration (stretch). The C-O bond is more polar and will thus experience a greater change in dipole moment during a stretching vibration, giving a more intense absorption.

b. Which would give a stronger C=C stretch in an IR spectrum, 1-butene or 2-butene? Why?

Intensity of absorption is correlated to change in dipole moment with the vibration (stretch). The 2-butene is symmetrical and will not experience a change in dipole moment during a stretching vibration. The 1-butene is not symmetrical about the C=C bond, and will this give a small change in dipole during stretching vibration and this the more intense absorption.

c. Which would have a higher frequency absorption, an N-H bond or a P-H bond? Why?

Absorption frequency is correlated to bond strength and atomic masses. Phosphorus is a larger atom than nitrogen, giving it a larger mass and weaker bonding via 3rd shell valence orbitals compared to nitrogen’s 2nd shell valence orbitals. Both of these factors cause the N-H bond to have a higher frequency absorption than the P-H bond.

2. Infrared Spectroscopy (continued)

Cyclohexene - Presence of C=C at 1600 cm-1 - Absence of C=O around 1700 cm-1 - Absence of O-H around 3300 cm-1

Cyclohexenol - Presence of O-H at 3300 cm-1 - Absence of C=O around 1700 cm-1 - Absence of C=C around 1600 cm-1

Cyclohexanone - Presence of C=O at 1700 cm-1 - Absence of C=C around 1600 cm-1 - Absence of O-H around 3300 cm-1

O

OH

3. Ultraviolet SpectroscopyO

O

O

O

OH

O

O

3. Ultraviolet Spectroscopy (cont.)

12

34

This would have the largest molar absorptivity (ε) and thus the most intense absorption

4. NMR Spectroscopya. If an average carbon requires irradiation at 75 MHz to resonate in a 7.046 T

magnetic field, what frequency will be required to resonate an average carbon in a 14.092 T magnetic field?

ν = γB0 so doubling the magnetic field doubles the frequency needed to flip the same nucleus, 2π therefore 150 MHz is needed.

b. Use the following molecule to answer the following.

Cla

b

c

d

Which carbon is furthest downfield?_____d_____

Which carbon is furthest upfield?_____a_____

Which carbon resonates at the highest frequency?_____d_____

Which carbon resonates at the highest chemical shift?_____d_____

Which carbon resonates at the lowest chemical shift?_____a_____

Which carbon is the most shielded?_____a_____

Which carbon is the most deshielded?_____d_____

4. NMR Spectroscopy (cont’d)Br

ClCl CH3

OOCH3

O

3 5 5 6 5

7 6 3 4 7

020406080100120140PPM

4. NMR SpectroscopyBr

Cl

Cl CH3

OOCH3

O

3 5 5 5 5

7 8 3 3 5

O O

Cl

OF

CH3

HO

s

dt

q m (7) t

t

m (dq)

ds

t

q

s

s

dd

t

t

m (dq)

4. NMR Spectroscopy

0123PPM

2H

3H

2H

3H

OCH3

O