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UNEQUAL COUPLING UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS
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UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

Dec 22, 2015

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Amice Holt
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Page 1: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

UNEQUAL COUPLINGUNEQUAL COUPLING TREE DIAGRAMSTREE DIAGRAMS

SPLITTING DIAGRAMS

aka “TREE” DIAGRAMS

Page 2: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

WHERE DOES THE N+1 RULE WORK ?WHERE DOES THE N+1 RULE WORK ?

The n+1 rule works only for protons in aliphatic chainsand rings, and then under special conditions.

1) All 3J values must be the same all along the chain.

There are two requirements for the n+1 rule to work:

2) There must be free rotation or inversion (rings) to make all of the hydrogens on a single carbon be nearly equivalent.

Page 3: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

CH

HCH

HCH

H3Ja = 3Jb

Hydrogens can interchange theirpositions byrotations aboutthe C-C bonds.

All the couplings along the chain have the same J value.

THE TYPICAL SITUATION WHERE THE n+1 RULE APPLIES

This makes all thehydrogens on eachof the carbon atomsequivalent.

Page 4: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

WHAT HAPPENS WHEN THE J VALUES ARE NOT EQUAL ?

CH

HCH

HCH

H3Ja

3Jb

3Ja = 3Jb

In this situation each coupling must be consideredindependently of the other.

A “splitting tree” is constructed

Page 5: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

CH

HCH

HCH

H7 Hz 3 Hz

USE THESE VALUESUSE THESE VALUES

Page 6: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

CH

HCH

HCH

H3Ja = 7

-CH2-CH2-CH2-

CONSTRUCTING A TREE DIAGRAMCONSTRUCTING A TREE DIAGRAM

The largest J value is usually used first.

SPLITTING FROM HYDROGENS TO THE LEFT

The next splittings will be added to each leg of the first splitting.

LEVEL ONE

Two neighbors givesa triplet.

Each level of thesplitting uses then+1 rule.

Page 7: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

CH

HCH

HCH

H3Ja = 7

-CH2-CH2-CH2-

CONSTRUCTING A TREE DIAGRAMCONSTRUCTING A TREE DIAGRAM

CH

HCH

HCH

H3Jb = 3

triplet of triplets

ADD SPLITTING FROM HYDROGENS TO THE RIGHT

The smaller splittingis used second.

FIRST LEVEL

SECOND LEVEL LEVEL TWO

It is also a triplet.EACH LEG OF LEVEL ONE IS SPLIT

Page 8: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

WHEN BOTH 3J VALUES ARE THE SAME

-CH2-CH2-CH2-

….. because of overlapping legs.You get the quintet predicted bythe n+1 rule.

The n+1 rule is followed …..

n+1 = (4 + 1) = 5

Splitting fromhydrogens onthe left

Splitting fromhydrogens onthe right

Splittingsoverlap

1:2:11:2:1

1:2:11:2:1

1:4:6:4:1

INTENSITIES

+

LEVEL ONE

LEVEL TWO

WHEN THE n+1 RULE APPLIES WE CAN JUMP TO THE FINAL RESULT - NO TREE NEEDED

Page 9: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

2-PHENYLPROPANAL2-PHENYLPROPANAL

A case where there are unequal J values.

Page 10: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

Spectrum of 2-Phenylpropanal

J = 2 Hz

J = 7 Hz

a

b

c

d

CHCH3 CHO

a b d

c TMS

Page 11: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

CHCH3 CHO

3J1 = 7 Hz

7 Hz 2 Hz

3J2 = 2 Hz

the methine hydrogen is split by two different3J values.

Rather than the expectedquintet …..

ANALYSISANALYSISOF METHINEOF METHINEHYDROGEN’SHYDROGEN’SSPLITTINGSPLITTING

quartet by -CH3

doubletby -CHO

quartet of doublets

Page 12: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

PURE ETHANOLPURE ETHANOL

Page 13: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

ETHANOLETHANOLOld sampleRapid exchange catalyzedby impurities

quartet

triplet

broadsinglet

HO-CH2-CH3

hydrogen on OHis decoupled

400 MHz

Page 14: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

ETHANOLETHANOLUltrapure sample (new)Slow or no exchange

tripletdoublet ofquartets

triplet400 MHz

expansion expansion

Page 15: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

quartet of doublets

J = 7

J = 5

triplet triplet

J = 7J = 5

Page 16: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

VINYL ACETATEVINYL ACETATE

ALKENE HYDROGENS

Page 17: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

• 3J-cis = 8-10 Hz • 3J-trans = 16-18 Hz

• protons on the same carbon 2J-geminal = 0-2 Hz H

H

HH

H

H

PROTONS ON C=C DOUBLE BONDSPROTONS ON C=C DOUBLE BONDSCOUPLING CONSTANTS

For protons on saturated aliphatic chains 3J 8 Hz

Page 18: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

NMR Spectrum of Vinyl Acetate

CH3 C

O

O CH CH2

60 MHz

Page 19: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

Analysis of Vinyl AcetateAnalysis of Vinyl Acetate

HC HB HA

CCHH33 CC

OO

OOCC

HHCC

CCHHAA

HHBB

3JBC

3JAC

3JAC3JBC

2JAB2JAB

trans trans

cis

cis

gem gem

3J-trans > 3J-cis > 2J-gem

Page 20: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

2,4-DINITROANISOLE2,4-DINITROANISOLE

BENZENE HYDROGENS

Page 21: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

2,4-DINITROANISOLE2,4-DINITROANISOLE

400 MHz

9.0 8.0 7.0

Page 22: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

2,4-DINITROANISOLE2,4-DINITROANISOLE

8.72 ppm 8.43 ppm 7.25 ppm

Page 23: UNEQUAL COUPLING TREE DIAGRAMS TREE DIAGRAMS SPLITTING DIAGRAMS aka “TREE” DIAGRAMS.

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