Question

17. a. Draw the transition state and product structures for the reaction below. " Br + DMF Nao b. How would the reaction rate change if Br were changed to CI ? (1 mark) Increase Decrease Stay about the same C. How would the reaction rate change if CH3 CH2Br were changed to CH3Br? (1 mark) Increase Decrease Stay about the same d. How would the reaction rate change if more NaOCH CH2 were added? (1 mark) Increase Decrease Stay about the same e. How would the reaction rate change if NaOCH2CH3 were changed to NaSCH2CH3 ? Increase Decrease Stay about the same f. How would the reaction rate change if the solvent were changed to ethanol (CH3CH2OH) Increase Decrease Stay about the same

I'm not sure how to get the transition state and how to get the product. The mechanism is giving me a hard time.

Answer 1

a. The above given reaction is an example for the SN2 reaction mechanism, in which the attack of the nucleophile (ethoxide ion) from the rear side of the Bromine atom on the substrate, the reaction proceeds through the transtition state formation which is given below,
BY KH ©o Transition state + Bre Na Dietheyl ether

b. The rate of the reaction of SN2 reaction depends upon the Nature of the leaving group, if the presence of the better leaving group then the rate of the reaction will be faster.

Leaving tendency of the halogens: I>Br>Cl>F, this shows that when replacing the bromine with chlorine then rate of the reaction will be decreased.

c. The rate of the SN2 reaction is also depends upon the carbon skeleton of the substrate, if the skeleton has high in bulk then rate of the reaction will be slower, but the given condition here is replacing of the high bulk ethylbromide with less bulk methyl bromide, then the rate of the reaction will be Increased considerably.

d. The rate of the SN2 reaction depends upon the concentration the both substrate and the nucleophile, when any one of the concentration is increased then the rate of the reaction is also increased, here when more nucleophile(sodium ethoxide) is added the rate of the reaction is also increased.

e. The rate of the SN2 reaction is increased, when the nucleophilicity of the nucleophile is increased, the nucleophilicity of the NaSCH2CH3 is higher than that of the sodium ethoxide, So the rate of the reaction will be increased when NaSCH2CH3 is used.

f. When using the aprotic solvent in the SN2 reaction the rate of the reaction will be increased, but as given condition, ethanol is the polar protic solvent so the rate of the reaction will be decreased considerably.