- Joined
- Apr 29, 2013
- Messages
- 31
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- 39
Hi guys,
The question asks:
The greatest amount of energy is required to break which of the following carbon-carbon bonds?
A) H3C--CH3
B) (H3C)3C--C(CH3)3
C) H2C=CH2
D) (H3C)2=C(CH3)2
The solution states the answer is D.
How I went about thinking about this question:
Double bonds are stronger than single bonds. This eliminates A and B.
Between C and D, the difference is substitution of the carbons to which the bond is attached.
Substituted carbons create weaker bonds. My justification for this: think of a primary carbon-hydrogen, and a tertiary carbon-hydrogen bond. With a homolytic (radical) cleavage of both bonds, the tertiary carbon product would be more stable than the primary carbon product, due to the fact that the tertiary carbon has more carbon substituents that are electron donating and can stabilize the radical. Thus since the tertiary carbon product is more stable, its bond with hydrogen is weaker.
Using the same logic to this problem, in C you have a primary carbon breaking a double bond, and in D, you have a tertiary carbon breaking a double bond. The tertiary carbon's bond should be weaker right?
I'm worried about this because I've completely thought out my logic and still gotten to the wrong answer.
Please help clarify this for me.
Thank you,
The question asks:
The greatest amount of energy is required to break which of the following carbon-carbon bonds?
A) H3C--CH3
B) (H3C)3C--C(CH3)3
C) H2C=CH2
D) (H3C)2=C(CH3)2
The solution states the answer is D.
How I went about thinking about this question:
Double bonds are stronger than single bonds. This eliminates A and B.
Between C and D, the difference is substitution of the carbons to which the bond is attached.
Substituted carbons create weaker bonds. My justification for this: think of a primary carbon-hydrogen, and a tertiary carbon-hydrogen bond. With a homolytic (radical) cleavage of both bonds, the tertiary carbon product would be more stable than the primary carbon product, due to the fact that the tertiary carbon has more carbon substituents that are electron donating and can stabilize the radical. Thus since the tertiary carbon product is more stable, its bond with hydrogen is weaker.
Using the same logic to this problem, in C you have a primary carbon breaking a double bond, and in D, you have a tertiary carbon breaking a double bond. The tertiary carbon's bond should be weaker right?
I'm worried about this because I've completely thought out my logic and still gotten to the wrong answer.
Please help clarify this for me.
Thank you,