CHEM QUESTION

2011-09-05 4:03 am

An acyclic hydrocarbon X was found to contain 85.6% carbon and 14.4% hydrogen by mass. When 0.07g of X wasintroduced into a gas syringe at room temperature and pressure, its volume wasfound to be 20.0cm^3. There are two structural isomers, A and B, of X. They bothhave the following properties:(I)A hashigher melting point between the two of its structural isomers.(II)B isoptically active. (a)Determinethe molecular formula of X.(b)Deducethe structure of A and comment on its high melting point.(c) Deducethe structure of B and explain why it is optically active.(r.a.m. :H=1.0, C=12.0, molar volume of a gas at r.t.p.=24dm^3 )

回答 (1)

知識就是力量

2011-09-05 4:35 am

✔ 最佳答案

(a) Mass ratio (C to H) = 0.856 : 0.144 = 5.944 : 1
Mole ratio (C to H) = 5.944/12 : 1 = 0.4953 : 1 = 1 : 2
Empirical formula for X = CH2 (i.e. this does not exist)
No. of moles of X = 0.02/24 = 8.33*10^-4 mol
Molar mass of X = 0.07/8.33*10^-4 = 84.0 g/mol
Let (CH2)n be the molecular formula for X
n(12 + 2) = 84
n = 6
Thus molecular formula for X is C6H12.

Hint for (b): The structure of X should adopt a trans-configuration.

Hint for (c): The structure of X should adopt a enantiomer.

2011-09-04 20:35:55 補充：
Typo
Hint for (c): The structure of X should be an enantiomer.

2011-09-04 20:53:38 補充：
Typo:
Hint for (b): The structure of A should adopt a trans-configuration.

Hint for (c): The structure of B should adopt a enantiomer.

參考: Knowledge is power.

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