 Solution

ID: past-exam-of-the-mphil-in-micro-and-nanotechnology-enterprise-course-of-the-university-of-cambridge/2023/paper-1/section-b/10/ii/a/solution

 Top articles  Latest articles New article in topic

Past exam of the MPhil in micro- and nanotechnology enterprise course of the University of Cambridge / 2023 / Paper 1 / Section B / 10 / ii / a / Solution by

Codex  0 2026-10-20

The products are

B = H C \equiv C - C (C H_{3})_{2} - OC H_{2} C H_{3},

(1)

D = 3 - Cl C_{6} H_{4} - C H_{2} - OC H_{2} C H_{3} .

(2)

B retains the terminal alkyne and replaces the tertiary propargylic chlorine with ethoxy. D replaces the benzylic chlorine while retaining the aromatic chlorine; its meta arrangement follows from the drawn starting material, rather than from four aromatic protons alone.

Product	Proton shift / ppm	Assignment
B	1.21, 3H triplet	Ethoxy terminal methyl, coupled to the adjacent two protons.
B	1.46, 6H singlet	Two equivalent methyl groups on the substituted carbon, with no neighboring proton to split them.
B	2.66, 1H singlet	Terminal alkyne proton.
B	3.59, 2H quartet	Ethoxy methylene next to oxygen, coupled to its methyl group.
D	1.18, 3H triplet; 3.58, 2H quartet	The ethoxy group, with a common approximately 7 Hz coupling.
D	4.80, 2H singlet	Benzylic methylene attached to oxygen, with no vicinal aliphatic proton.
D	Two aromatic multiplet regions, 4H total	The four remaining ring protons of the disubstituted aromatic ring.

For B, the strong

3300 c m^{- 1}

band is the terminal sp C–H stretch, the

2950 c m^{- 1}

band is aliphatic C–H stretching, and the weak

2100 c m^{- 1}

band is the alkyne stretch. The terminal proton and alkyne band together distinguish this from an alcohol interpretation of the high-frequency absorption.

For D,

3050 c m^{- 1}

is aromatic C–H stretching,

2950 c m^{- 1}

is aliphatic C–H stretching, and the

1600

and

1580 c m^{- 1}

bands are aromatic skeletal stretches. The listed spectrum is a selected peak list, so omission of a C–O band is not evidence that the ether bond is absent.

Figure 1.
Derived ether products and the competing elimination product
. Original skeletal drawings of B, D and F. B and D retain the unsaturation indicated by the spectral data; F is the conjugated enyne formed by loss of hydrogen chloride from the tertiary propargylic substrate. **Details**.

 Read the full article

 New to topics? Read the docs here!