Question

Answer the following with regards to the preparation of a haloalkane from an alcohol:

In the experiment performed, the reaction was of tert-butyl alcohol with concentrated hydrochloric acid resulted to tert-butyl chloride and water as a by-product was observed:

A. Why do primary and secondary alcohols undergo S_N1 reaction mechanisms while tertiary alcohols react via S_N2 reaction mechanisms? Explain.

B. Will the reaction between hydrochloric acid and phenol produce chlorobenzene? Why, or why not? Explain.

C. What products would you expect from the reaction of t-butyl chloride with each of (i) methanol; (ii) butanethiol; (iii) acetic acid?

D. In the experiment, why was there a need to wash the solution with sodium bicarbonate, water and saturated sodium chloride? A flow chart may be used to present the answer.

Answer the following questions with regards to kinetic vs thermodynamic control of reaction pathways:

In this experiment, the reaction of cyclohexanone with semicarbazide giving off cyclohexanone semicarbazone and the reaction of 2-furaldehyde with semicarbazide giving off 2-furaldehyde semicarbazone were observed:

E. Which of the semicarbazones is the kinetic product and which is the thermodynamic product? What experimental evidence supports this?

F. Draw a simplified reaction coordinate profile to depict the energy pathways of the cyclohexanone versus furfural reaction with semicarbazide.

G. If you repeated the conditions for the competitive semicarbazone formation from cyclohexanone and 2-furaldehyde under thermodynamic control but place the flask in the freezer for 1 week rather than in a dry place, what would you expect the result be?

Answer 1

Answer the following with regards to the preparation of a haloalkane from an alcohol:

In the experiment performed, the reaction was of tert-butyl alcohol with concentrated hydrochloric acid resulted to tert-butyl chloride and water as a by-product was observed:

A.    Why do primary and secondary alcohols undergo S_N1 reaction mechanisms while tertiary alcohols react via S_N2 reaction mechanisms? Explain.

The statement made above is not true; it’s actually the other way round. Primary and secondary alcohol undergo S_N² reaction because the carbocation formation is not favored and it is less crowded, so electrophilic carbon can be approached by the nucleophile easily.. But in case of tertiary alcohol, the carbocation forms is a tertiary one, which is stabilized by the inductive effect of the three methyl group and the reaction follow an S_N¹ mechanism.

B.      Will the reaction between hydrochloric acid and phenol produce chlorobenzene? Why, or why not? Explain.

In phenol, the OH is attached to an sp2 carbon and simple substitution at sp2 center is not possible.