Question 1

Which of the following is the major product when the alkyl halide shown below undergoes an E1 elimination reaction?

$$	ext{(Structure: 1-chloro-1,1-dimethylethylbenzene)}$$

Accepted Answer

The only product is the alkene formed by elimination at the benzylic position (see image 2).

Question 2

Given the following reaction: $$	ext{Cyclopentyl tosylate + NaN}_3 in $$DMSO, which mechanism does this reaction most likely follow?

Accepted Answer

SN2

Question 3

Consider the following two reactions:
(a) Cyclopentanol (protonated) forms a carbocation and water.
(b) Cyclopentyl bromide forms a carbocation and bromide ion.
For which reaction would the rate of carbocation formation be higher?

Accepted Answer

The rate of carbocation formation will be higher in reaction (a).

Question 4

Given a molecule with two non-equivalent beta carbons, how does the presence of multiple beta hydrogens influence the number of possible elimination products?

Accepted Answer

The presence of multiple beta hydrogens can lead to multiple elimination products.

Question 5

Arrange the following compounds in increasing order of their E2 reactivity:
(i) trans-1-ethyl-2-chlorocyclohexane
(ii) cis-1-ethyl-2-chlorocyclohexane
(iii) 1-ethyl-1-chlorocyclohexane

Accepted Answer

(iii) \u003c (i) \u003c (ii)

Question 6

In the synthesis of 2,3-dihydrobenzo[b][1,4]dioxine-2,3-dicarboxylic acid, which intermediate forms faster, A or B?

Accepted Answer

A would form faster than B.

Question 7

Which of the following substitution reactions occurs at a faster rate and why?
(i) 2-chloro-2-methylpentane with ethanol
(ii) 2-chloro-2-methylpentane with acetic acid

Accepted Answer

Reaction (i) occurs at a faster rate because it involves a less sterically hindered nucleophile.

Question 8

When 4-chloro-3-ethyl-4-methylheptane reacts via the E2 mechanism, which stereoisomer is obtained in the greatest yield?

Accepted Answer

The E-isomer with the most substituted double bond (see image 14).

Question 9

Use the rule of 13 to provide the molecular formula of a compound that contains C, H, and two O with $$M^+ = 118.$$

Accepted Answer

C$$_6H$_{12}O$_2$$

Question 10

Predict the important peaks present in the IR spectrum of the following molecule (see image 18):

Accepted Answer

Medium intensity bands at approximately 3300 cm$$^{-1}$$ and 3150 cm$$^{-1}$$ for N-H bond stretching (primary amine), a strong and sharp band at 3333-3267 cm$$^{-1}$$ for C-H bond stretching (alkyne), a weak to medium intensity band at 2260-2190 cm$$^{-1}$$ for C≡C bond stretching (alkyne), and a medium intensity band at 3000-2840 cm$$^{-1}$$ for C-H bond stretching (alkane)

Question 11

Determine the functional group present in a compound that has a chemical formula of C$$_6H$_{14}O $$and an IR spectrum with a broad peak around 3300 cm$$^{-1}.$$

Accepted Answer

Alcohol

Question 12

Why is mastering analytical techniques important for organic chemistry students?

Accepted Answer

It is essential for laboratory applications and exam success.

Question 13

Apart from using the molecular mass, how else can you determine that the fragment peak at $$m/z = 63 in $$the mass spectrum for 1-bromo-2-chloroethane includes chlorine, not bromine?

Accepted Answer

The 3:1 ratio of M and M+2 peaks indicates that the fragment ion includes a chlorine atom.

Question 14

Sketch the signal for an octet in $$^1H $$NMR and provide the ratio of its peaks.

Accepted Answer

1:7:21:42:42:21:7:1

Question 15

Determine the number of sets of equivalent protons present in the following molecule (see image 23).

Accepted Answer

Four sets

Question 16

Evaluate the effect of spatial arrangement on NMR shielding of protons in CH$$_3CH=$$CHCl and how it differentiates their signals.

Accepted Answer

The proximity to electronegative chlorine causes different shielding, leading to distinct NMR signals for protons.

Question 17

How many different NMR signals will be observed in the NMR spectrum of each of the following compounds theoretically? Determine the approximate chemical shift for each proton and highlight any diastereotopic relationships.
(i) PhCHClCH$$_2Cl
(ii) $$vinyl bromide

Accepted Answer

See image 24: Diastereotopic protons H$$_d$$ and H$$_f$$; chemical shifts: H$$_a 4.2 $$ppm, H$$_b 4.2 $$ppm, H$$_c 5.0 $$ppm, H$$_d 3.6 $$ppm, H$$_e 3.6 $$ppm, H$$_f 2.3 $$ppm.

Question 18

If a compound has a molecular formula C$$_4H$_{10}$$ and shows 3 signals in the proton NMR spectrum, what does this indicate about the molecule's symmetry?

Accepted Answer

The molecule has some symmetry.

Question 19

For the hydrogen indicated in red in the following structure (see image 28), sketch the expected $$^1H $$NMR signal showing its estimated chemical shift.

Accepted Answer

See image 29: Multiplet centered around 4.50 ppm.

Question 20

Draw the DEPT sequence spectra expected for the molecule given below (see image 33).

Accepted Answer

See image 35: DEPT-90 shows only CH, DEPT-135 shows CH and CH$$_3 as $$positive, CH$$_2 as $$negative.

E1 Mechanism: Predicting the Product of Alkyl Halide Elimination

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