One mole of methyl 5-phenylpent-4-en-2-ynoate, $C X_{6} H X_{5} - CH = CH - C \equiv C - COOCH X_{3}$ , is hydrogenated with $H X_{2}$ (1 atm) over Pd-C at room temperature until no more gas is absorbed. Under these conditions only C=C and C#C bonds react (the ester group and the benzene ring are unchanged). How many moles of $H X_{2}$ are absorbed? Give an integer.

Numerical answer type, tolerance 0.5.

Answer: 3

One C=C takes 1 mol of

H X_{2}

and the C#C takes 2 mol (alkyne to alkane). Ester and benzene ring do not react. Total = 1 + 2 = 3 mol.