how many peaks in the 13c nmr spectra? - chemistry · how many peaks in the 13c nmr spectra? oh ohf...

How many peaks in the 13C NMR spectra?

OH OHFOHFF

2 3 4 3

ClFHOClFCl ClClCl

6 4 2

Which compound matches this 13C NMR spectrum?BrBrBr

BrBrBr

BrBrBr

BrBrBr

OOH

AB

C

O

A

BC

Br B

CA

Rank the labeled C’s of each compound in order of increasingchemical shift?

B ~ 33ppm

C ~ 35ppm

A ~ 115ppm

A ~ 8ppm

B ~ 37ppm

C ~ 210ppm

C ~ 9ppm

B ~ 30ppm

A ~ 177ppm

NO

O

OH

NO

A compound has a 13C NMR spectrum with three peaks and the IRspectrum below, choose the correct compound.

Information gained from a 1H NMR Spectrum

• Number of Signals

• Position of Signals

• Intensity of Signals

• Spin-Spin Splitting of Signals

How many different types of protons are in each compound?

H3COCH3

HAHA

1 type

H3CH2CCl

HA

HB

2 types

H3CH2COCH3

HA

HB

HC

3 types

H3CCHH3CCH2H2CCH3

HA

HA

HB

HC

HD

HE

5 types

Determining the number of different protons in compoundswith π bonds.

ClClHH cis to Cl

cis to Cl

1 type

ClBrHH cis to Cl

cis to Cl

2 types

ClHHHcis to Cl

cis to H

3 types

Determining the number of different protons in compounds withrings..

HHHHHH

All H’s areequivalent, 1 type

HHHHClHcis to Cl

cis to H3 types

HHHHCH3CH3

Protons onmethylsareequivalent

Each ofthese is cisto amethyl 2 types

If two protons attached to the same carbon can be replacedseparately with a common group such as a Z group which resultsin creating two molecules that are enantiomers to one another, inother words they are non-superimposible mirror images, theseprotons are called enantiotopic protons.

Enantiotopic Protons

If two protons attached to the same carbon can be replacedseparately with a common group such as a Z group which results increating two molecules that are diastereomers, these protons wouldbe diastereotopic protons. Such protons will generate nmr signals atslightly different chemical shifts.

Diasterotopic Protons

OOOOH

OO HOOH

Spin-SpinCoupling

When determining the spin-spin coupling, look at the number ofprotons on the adjacent carbon. For the methyl group, look at themethylene group. There are 2 protons, so using the N+1 rule tells usthat the peak should be a triplet in a 1:2:1 ratio.

For the methylene group, look at the methyl group. There are 3protons, so using the N+1 rule tells us that the peak should be aquartet in a 1:3:3:1 ratio.

Protons attached via a double bond show a unique splittingpattern., a doublet of doublets.

O

HO

⇑

Hc

⇑

Ha

⇑

HbN+1=4+1=5

OOH

O

OH