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Chapter 12: Q.20P (page 638)

Question: (A true story.) While organizing the undergraduate stockroom, a new chemistry professor found a half-gallon jug containing a cloudy liquid (bp 100鈥�105 掳C), marked only 鈥淪TUDENT PREP.鈥� She ran a quick mass spectrum, which is printed below. As soon as she saw the spectrum (without even checking the actual mass numbers), she said, 鈥淚 know what it is.鈥�

(a) What compound is the 鈥渟tudent prep鈥�? Any uncertainty in the structure?

(b) Suggest structures for the fragments at 136, 107, and 93. Why is the base peak (at m/z 57) so strong?

Short Answer

Expert verified

Answer

a. The compound student prep is 1-bromobutane.

b. The fragmentation pattern is:

Step by step solution

01

Mass spectrum

A graph between the intensity (abundance) and mz (mass to charge ratio) values of the ions is known as the mass spectrum.

02

Explanation for part (a)

The unknown compound will be 1-bromobutane since there are two equal peaks as seen for M+and M+2 in the mass spectrum.

03

Explanation for part (b)

The fragmentation pattern is shown below:

The base peak at is formed by leaving bromine (Br) , hence it is strong.

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Most popular questions from this chapter

Predict the characteristic infrared absorptions of the functional groups in the following molecules.

(a) cyclopentene

(b) hexan-2-ol

(c) hexan-2-one

(d) hex-1-yne

(e) dimethylamine

(f) hexanoic acid

(g) hexanenitrile

(h) methyl acetate

(i) hexanamide.

Predict the masses and the structures of the most abundant fragments observed in the mass spectra of the following compounds

a. 2-methylpentane

b. 3-methylhex-2-ene

c. 4-methylpentane-2-ol

d. 2-methyl-1-phenylpropane

e. Cyclohexylisopropy; ether [cyclohexyl--O-CH(CH3)2 ]

f. CH3CH2CH2NHC(CH3)2

g.

h.3-bromo-2-methylpentane

Convert the following infrared wavenumbers into wavelengths.

(a) 1600cm-1, typical for an aromatic

(b) 3000cm-1, typical for a saturated bond

(c) 1715cm-1, typical for a ketone carbonyl

(d) 1750cm-1, typical for an ester carbonyl

(e) 2220cm-1, typical for a nitrile

(f) 3300cm-1, typical for an alcohol

Show the fragmentations that give rise to the peaks at m/z 43, 57, and 85 in the mass spectrum of 2,4-dimethylpentane (Figure 12-17).

For each hydrocarbon spectrum, determine whether the compound is an alkane, an alkene, an alkyne, or an aromatic hydrocarbon, and assign the major peaks above (to the left of) 1600 cm-1 . More than one unsaturated group may be present.
See all solutions

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