How many dipeptides can be formed in the reaction below? QUESTION 15 Which of th

Question

How many dipeptides can be formed in the reaction below? QUESTION 15 Which of the following correctly explains how sulfuric acid catalyzes the reaction shown below? The acid increases the rate of nucleophile elimination. The acid increases the nucleophilicity of the alcohol. The acid donates a proton to the alcohol. The acid converts the ester into a carboxylic acid. The acid activates the carbonyl carbon and makes more electrophilic. QUESTION 16 Which of the following s not part of the mechanism for the catalytic hydrogenation of an alkene Adsorption of hydrogen gas onto metal surface. Formation of C?H bond and liberation of C atom from surface. Adsorption of alkene onto metal surface. Proton transfer from metal to carbon. liberation of alkane from surface.

Explanation / Answer

part I

The numbder of dipeptides thegiven two aminoacids can form is four.If we take the two AAs as P and Q, N-terminal f P combining with c- terminal of Q to give PQ as dipepeptide and N-terminal of q combines with C-terminal of P giving QP as dipeptide. and the remaining two are self reaction products that is PP and QQ. The side chain amide or alcohol have no role in peptide formation.

Q15)

The given reaction is transesterification, which follows exactly the ester formation mechanism, in which the carbonyl carbon acts as electrophile and the alcohol is the nucleophile. Thus the presence of sulphuric acid is to protonate the carbonyl carbon and making it more electrophilic fr the nucleophilic acyl substitution reaction.

Thus the fifth option is correct.

Q16)

Catalytic hydroenation of an alkene involves

     i) adsorption of hydrogen on metal surface      ii) the alkene approaches it and forms C-H bonds

    iii) transfer of H atoms to the alkene              iv)once the alkane is formed it liberates from the surface of metal

thus the correct option(incorrect about mechanism ) is third option -adsorption of akene onto metal surface. The mechanism does not involve adsorption of alkene on metal.

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