IR Spectroscopy Unknowns – GTF’s version

last updated on Thursday, June 1, 2000

Problem Set Answer Key

Acceptable Choices Actual Compound

1.
cyclohexanone, 2–heptanone, 2,5-hexanedione 2–heptanone
Difficult to distinguish from cyclohexanone and 2,5-hexanedione

2.
acetophenone acetophenone

3.
1–pentanol 1–pentanol
Methanol can be ruled out based on CH₂ bending absorption present at 1461 cm^-1.

4.
methyl benzoate methyl benzoate

5.
diethyl maleate diethyl maleate

6.
cyclohexanone, 2–heptanone, 2,5-hexanedione cyclohexanone The carbonyl absorption is at 0.98 % transmittance. Thus, the spectrum is offscale. The OH strietch at ~3400 is most likely due to the trace amounts of the hydrate present. [note: carbonyl compounds are in equilibrium with their hydrate form. If the IR is off scale, then the hydrate OH absorption is typically observable]. Difficult to distinguish from 2-heptanone and 2,5-hexanedione

7.
ethyl acetoacetate ethyl acetoacetate Has both ester (1744 cm^-1) and keto (~1710 cm^-1) functionality.

8.
o-tolunitrile or p-tolunitrile o-tolunitrile Difficult to differentiate from p-tolunitrile.

9.
benzyl alcohol benzyl alcohol

10.
cyclohexanone, 2–heptanone, 2,5-hexanedione 2,5-hexanedione Difficult to distinguish from 2-heptanone and cyclohexanone

11.
1-heptyne 1-heptyne

12.
2-heptyne or hexane 2-heptyne Difficult to differentiate from hexane. Carbon-carbon triple bonds is very weak and not observed.

	Acceptable Choices	Actual Compound
1.	cyclohexanone, 2–heptanone, 2,5-hexanedione	2–heptanone	Difficult to distinguish from cyclohexanone and 2,5-hexanedione
2.	acetophenone	acetophenone
3.	1–pentanol	1–pentanol	Methanol can be ruled out based on CH₂ bending absorption present at 1461 cm^-1.
4.	methyl benzoate	methyl benzoate
5.	diethyl maleate	diethyl maleate
6.	cyclohexanone, 2–heptanone, 2,5-hexanedione	cyclohexanone	The carbonyl absorption is at 0.98 % transmittance. Thus, the spectrum is offscale. The OH strietch at ~3400 is most likely due to the trace amounts of the hydrate present. [note: carbonyl compounds are in equilibrium with their hydrate form. If the IR is off scale, then the hydrate OH absorption is typically observable]. Difficult to distinguish from 2-heptanone and 2,5-hexanedione
7.	ethyl acetoacetate	ethyl acetoacetate	Has both ester (1744 cm^-1) and keto (~1710 cm^-1) functionality.
8.	o-tolunitrile or p-tolunitrile	o-tolunitrile	Difficult to differentiate from p-tolunitrile.
9.	benzyl alcohol	benzyl alcohol
10.	cyclohexanone, 2–heptanone, 2,5-hexanedione	2,5-hexanedione	Difficult to distinguish from 2-heptanone and cyclohexanone
11.	1-heptyne	1-heptyne
12.	2-heptyne or hexane	2-heptyne	Difficult to differentiate from hexane. Carbon-carbon triple bonds is very weak and not observed.