Under given conditions, 1 g of methane diffuses in 20 s. Under the same conditions, sqrt(20) g of an open-chain hydrocarbon A diffuses in 40 s. A 10 mg sample of A consumes 8.40 mL of H2 gas measured at 0 deg C and 760 mmHg. One open-chain isomer of A on ozonolysis gives only methanal and

Question

Under given conditions, 1 g of methane diffuses in 20 s. Under the same conditions, sqrt(20) g of an open-chain hydrocarbon A diffuses in 40 s. A 10 mg sample of A consumes 8.40 mL of H2 gas measured at 0 deg C and 760 mmHg. One open-chain isomer of A on ozonolysis gives only methanal and glyoxal. A six-membered stable monocyclic isomer of A on reductive ozonolysis CANNOT give which of the following products?

Accepted Answer

OHC-CH2-CH2-CH2-CHO. Graham's law applied to molar rates gives M_A = 80 g/mol (C6H8, degrees of unsaturation = 3, confirmed by 3 mol H2 per mol A at STP). The six-membered monocyclic isomer of C6H8 is cyclohexadiene (uses 1 degree for ring, 2 for double bonds). 1,3-cyclohexadiene gives OHC-CHO and OHC-CH2-CH2-CHO on reductive ozonolysis. 1,4-cyclohexadiene gives two molecules of OHC-CH2-CHO. The 5-carbon dialdehyde OHC-CH2-CH2-CH2-CHO would require 5 carbons in a chain between two aldehyde groups, impossible from a 6-membered ring where cutting two double bonds always leaves fragments summing to 6 carbons with smaller chains.

Solution

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