'x' is the product which is obtained &om propanenitrile and stannous chloride in the presence of hydrochloric acid followed by hydrolysis. 'y' is the product which is obtained from the but-2-ene by the ozonolysis followed by hydrolysis. From the followu1g, which product is not obtained when one mole of 'x' and one mole of 'y' react with, each other in the presence of alkali followed by heating?

We first identify the products $$x$$ and $$y$$.

Finding x: Propanenitrile ($$CH_3CH_2CN$$) is treated with stannous chloride ($$SnCl_2$$) and hydrochloric acid, followed by hydrolysis. This is the Stephen reduction, which converts a nitrile to an aldehyde. Therefore $$x = \text{propanal}\;(CH_3CH_2CHO)$$.

Finding y: But-2-ene ($$CH_3CH{=}CHCH_3$$) undergoes ozonolysis followed by hydrolysis. The double bond is cleaved to produce two molecules of ethanal (acetaldehyde, $$CH_3CHO$$). Since we take one mole of the ozonolysis product, $$y = \text{ethanal}\;(CH_3CHO)$$.

When one mole of propanal and one mole of ethanal react in the presence of alkali followed by heating, aldol condensation followed by dehydration takes place. Four $$\alpha,\beta$$-unsaturated aldehyde products are possible:

Product 1 — Self-aldol of ethanal: The enolate of one ethanal molecule attacks the carbonyl of another ethanal. After dehydration this gives $$CH_3CH{=}CHCHO$$, which is but-2-enal (crotonaldehyde).

Product 2 — Cross-aldol (ethanal enolate + propanal): The enolate of ethanal ($${}^{-}CH_2CHO$$) attacks the carbonyl carbon of propanal. The resulting aldol product dehydrates to give $$CH_3CH_2CH{=}CHCHO$$ = pent-2-enal.

Product 3 — Cross-aldol (propanal enolate + ethanal): The enolate of propanal ($$CH_3\overset{-}{C}HCHO$$) attacks the carbonyl carbon of ethanal. The aldol product dehydrates to give $$CH_3CH{=}C(CH_3)CHO$$ = 2-methylbut-2-enal.

Product 4 — Self-aldol of propanal: The enolate of one propanal attacks the carbonyl of another propanal. Dehydration gives $$CH_3CH_2CH{=}C(CH_3)CHO$$ = 2-methylpent-2-enal.

Now consider the options. 3-Methylbut-2-enal has the structure $$(CH_3)_2C{=}CHCHO$$. Forming this would require a branched reactant such as acetone or isobutyraldehyde as one of the starting materials, but neither is present in our reaction mixture. Therefore, 3-methylbut-2-enal cannot be obtained from this reaction.

Hence, the correct answer is Option 2.