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9NUCLEAR MAGNETIC RESONANCE AND
MASS SPECTROMETRY: TOOLS FOR
STRUCTURE DETERMINATION
SOLUTIONS TO PROBLEMS
9.1
OCH2CH3
CH3C
O
(a)(c)
(b)
(a) δ 0.8−1.10
(b) δ 2.1−2.6
(c) δ 3.3−3.9
9.2 The presence of two signals in the 1H NMR spectrum signifies two unique proton environ-
ments in the molecule. The chemical shift of the downfield signal, (a), is consistent with
protons and a chlorine on the same carbon. Its triplet nature indicates two hydrogens on the
adjacent carbon.
The upfield quintet (b) indicates four adjacent and equivalent hydrogens, which requires
two hydrogens on each of two carbons.
Integration data indicate a ratio of (approximately) 2:1, which is actually 4 : 2 in this
case.
Of the isomeric structures with the formula C3H6Cl2, only
ClCl
(a)(a)
(b)
fits the
evidence.
9.3 (a) We see below that if we replace a methyl hydrogen by Cl, then rotation of the methyl
group or turning the whole molecule end-for-end gives structures that represent the
same compound. This means that all of the methyl hydrogens are equivalent.
rotate CH2Cl group
turn
C
H
H
H
H
H
HC
C
H
H
H HC
Cl
H
C
H
H
Cl H
H
replace H with Cl
H
C
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