Question 11.3: Predicting Chemical Shifts in 1H NMR Spectra Methyl 2,2-dime...

Predicting Chemical Shifts in ^{1}H NMR Spectra

Methyl 2,2-dimethylpropanoate (CH_{3})_{3}CCO_{2}CH_{3} has two peaks in its ^{1}H NMR spectrum. What are their approximate chemical shifts?

Strategy
Identify the types of hydrogens in the molecule, and note whether each is alkyl, vinylic, or next to an electronegative atom. Then predict where each absorbs, using Table 11.3 if necessary.

TABLE 11.3
Correlation of  ^{1}H Chemical Shift with Environment
Type of hydrogen		Chemical shift (δ)	Type of hydrogen		Chemical shift (δ)
Reference	Si(CH_{3})_{4}	0	Alcohol	-\overset{|}{\underset{|}{C} } -O-H	2.5–5.0
Alkyl (primary)	-CH_{3}	0.7–1.3
Alkyl (secondary)	-CH_{2}-	1.2–1.6	Alcohol, ether	-\overset{\underset{|}{H} }{\underset{|}{C} } -O-	3.3–4.5
Alkyl		1.4–1.8
(tertiary)	-\overset{|}{CH} –		Vinylic		4.5–6.5
Allylic	C=C-\overset{\underset{|}{H} }{\underset{|}{C} } –	1.6–2.2
Methyl ketone	-\overset{\underset{||}{O} }{C} -CH_{3}	2.0–2.4	Aryl	Ar-H	6.5–8.0
Aromatic methyl	Ar-CH_{3}	2.4–2.7	Aldehyde	-\overset{\underset{||}{O} }{C}- H	9.7–10.0
Alkynyl	-C\equiv C-H	2.5–3.0	Carboxylic acid	-\overset{\underset{||}{O} }{C}- O-H	11.0–12.0
Alkyl halide	-\overset{\underset{|}{H} }{\underset{|}{C} } -Hal	2.5–4.0