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www.chemsheets.co.uk A2 032 17-Jul-12


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Protons and neutrons can be regarded as spinning about

their axis.

In many atoms these spins are paired against each other

and so the nucleus has no overall spin (e.g.12

C). In some atoms (e.g. 1H and 13C) the nucleus has an

overall spin.

A nucleus that spins generates a magnetic

field.

The direction of the magnetic field depends

which way the nucleus spins.



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Usually the two possible spin states of the nucleus have

the same amount of energy.

However, in a magnetic field, the two spin states have

different energies.

Energy Applied

magnetic

field

Magnetic field in

same direction as

applied field

Magnetic field

opposed to

applied field

Energy gap corresponds tofrequency of radiowaves



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butanone



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In a spectrum, there is one signal for each set of

equivalent H atoms.

The intensity of each signal being proportional to the

number of equivalent H atoms it represents.



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CH3 CH CH2 CH3

Br

CH3 CH CH2 CH2 CH3

Br

CH3 CH2 CH3 2 sets of equivalent Hs: ratio 6:2 (3:1)

CH3 C

CH3

CH2

OH

CH3

4 sets of equivalent Hs: ratio 3:1:2:3

5 sets of equivalent Hs: ratio 3:1:2:2:3

4 sets of equivalent Hs: ratio 6:1:2:3



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For each of the following compounds, predict the

number of signals and the relative intensity of the

signals.

a) methylpropene

b) propene

c) 2-chloropropane

d) propanone

e) methylamine

f) ethyl propanoate

g) 1,2-dibromopropane

h) dimethylethyl

propanoate

i) but-2-ene



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2 signals: ratio 6:2 (3:1)

C CH3

CH3

O

CH CH3CH3

Cl

CH2 C CH3

CH3

CH2 CH CH3

3 signals: ratio 2:1:3

2 signals: ratio 6:1

1 signal

CH3 CH2 C

O

O CH2 CH3

CH3

NH2

2 signals: ratio 3:2

4 signals: ratio 3:2:2:3



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3 signals: ratio 2:1:3

2 signals: ratio 6:2 (3:1)

CH CH3CH2

BrBr

CH3 CH2 C

O

O C CH3

CH3

CH33 signals: ratio 3:2:9

CH CHCH3 CH3



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Samples are dissolved in solvents free of1H atoms, e.g.

CCl4, CDCl3.

CH3

Si CH3

CH3

CH3

A small amount of TMS

(tetramethylsilane) is added to calibratethe spectrum.

It is used because:

its signal is away from all the others

it only gives one signal

it is non-toxic

it is inert

it has a low boiling point so is easy to remove www.chemsheets.co.uk A2 032 17-Jul-12


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8 7 6 5 4 3 2 1

chemical shift



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8 7 6 5 4 3 2 1

chemical shift



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The spectra are recorded on a scale known as thechemical shift (), which is how much the field is shifted

from the field for TMS compared to the field for TMS.

= Field for TMS - Field measured x 106

Field for TMS

The is a measure in parts per million (ppm) of how far the

magnetic field required for absorption is shifted away from

that for TMS.

012345678910

chemical shift (ppm)

The depends on what other atoms/groups are near the H

more electronegative groups gives a greater shift. www.chemsheets.co.uk A2 032 17-Jul-12


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Data from AQA datasheet


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number of signals and the relative intensity of the

signals.

a) but-1-ene

b) 1,2-dichloropropane

c) propanal

d) 2-methylpropan-2-ol

e) pentane

f) ethyl methylpropanoate



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a) but-1-ene

b) 1,2-dichloropropane

c) propanal

d) 2-methylpropan-2-ol

e) Pentane

f) ethyl methylpropanoate

CH3 CH2 CH CH2

CH2 CH CH3

Cl Cl

CH3 CH2 C

O

H

CH3 C CH3

OH

CH3

CH3

CH2

CH2

CH3

CH2

CH3 CH C

O

O

CH3

CH2 CH3


N b f i l


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Number of signals

Relative size

Chemical shift

CH3 CH2 C

O

H

CH3 CH C

O

O

CH3

CH2 CH3

a) propanal

b) ethyl methylpropanoate



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Coupling / Splitting / Multiplicity



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CH3 CH2 C CH3

O

0 H next door

singlet (s)

1 H next doordoublet (d)

2 H next doortriplet (t)

3 H next doorquartet (q)

more H next doormultiplet (m)



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signal singlet doublet triplet quartet

appearance

number of lines 1 2 3 4

number of Hsnext door

0 1 2 3

relative size 1:1 1:2:1 1:3:3:1



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CH3 CH C

O

O

CH3

CH2 CH3

C CH CH3

Br

CH3

Br

Br

CH3 CH2 CH3



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CH3

CH2

CH2

CH3



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CH3 CH2 CH2 CH3CH2

CH3 C

O

CH2CH2 C

O

CH3

CH3 C

O

CH2CH2 C

O

CH2 CH3



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CH3 CH2 OH



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But you dont couple to

Hs that are equivalent

Hs on Os



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Number of signals

Position of signals

Relative intensities

Splitting

how many different sets of

equivalent H atoms there are

information about chemicalenvironment of H atom

gives ratio of H atoms for peaks

how many H atoms on adjacent C

atoms



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number of signals, the relative intensity of the

signals, and the multiplicity of each signal.

a) methylpropene

b) propene

c) 2-chloropropane

d) propanone

e) methylamine

f) ethyl propanoate

g) 1,2-dibromopropane

h) dimethylethyl

propanoate

i) but-2-ene



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2 signals: ratio 6 : 2 (3 :1)

s s

C CH3CH3

O

CH CH3CH3

Cl

CH2 C CH3

CH3

CH2

CH CH3

3 signals: ratio 2 : 1 : 3

d m d

2 signals: ratio 6 : 1

d m

1 signal

CH3 CH2 C

O

O CH2 CH3

CH3

NH2

2 signals: ratio 3 : 2

t q

4 signals: ratio 3 : 2 : 2 : 3

t q q t



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3 signals: ratio 2 : 1 : 3

d m d

2 signals: ratio 6 : 2 (3 :1) d q

CH CH3CH2

BrBr

CH3 CH2 C

O

O C CH3

CH3

CH33 signals: ratio 3 : 2 : 9

t q s

CH CHCH3 CH3



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Number of signals


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Number of signals

Relative size

Chemical shift

Multiplicity

a) 1,2-dichloropropane

b) but-1-ene

CH3 CH2 CH CH2

CH2 CH CH3

Cl Cl



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13C NMR spectra are often simpler than 1H NMR spectra.

They give a lot of valuable information about the chemicalenvironment of C atoms (e.g. the difference between Catoms in C=O, C-N, C N, C-C, C=C, etc.).

There is one signal for each set of equivalent C atoms.

There is no coupling (unlike 1H NMR).

The size of signal is not relative to the number of equivalent

C atoms (unlike H atoms in

1

H NMR). As in 1H NMR, the chemical shift (d) is measured relative to

TMS.

Although deuterated solvents are usually used, there will be

a signal for any C atoms in the solvent. www.chemsheets.co.uk A2 032 17-Jul-12


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