orgo DAT questions

[RozhonDDS]

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can someone please help me on these practice orgo questions. thank you

which of the following free radicals is the most stable?
A. CH3*
B. (CH3)3C*
C. (CH3)2CH*
D. CH3CH2CH2*
E. CH3(CH2)8CH2*


Which of the following carbocations is (are) the most stable?
A. R2HC+
B. R3C+
C. H3C+
D. RH2C+
E. B and C are equally stable


Please explain, thank you everyone

 

[BentalScholar]

can someone please help me on these practice orgo questions. thank you

which of the following free radicals is the most stable?
A. CH3*
B. (CH3)3C*
C. (CH3)2CH*
D. CH3CH2CH2*
E. CH3(CH2)8CH2*


Which of the following carbocations is (are) the most stable?
A. R2HC+
B. R3C+
C. H3C+
D. RH2C+
E. B and C are equally stable


Please explain, thank you everyone

Well although every single Orgo book includes this, here it goes. Carbon groups adjacent to the Carbon on which the free electron or the +ve charge is on are considered electron releasing groups that stabelize the radical/cation. Thus the molecule with the most substituted C is the most stable. So the answers are : B and B.

 

[RozhonDDS]

Well although every single Orgo book includes this, here it goes. Carbon groups adjacent to the Carbon on which the free electron or the +ve charge is on are considered electron releasing groups that stabelize the radical/cation. Thus the molecule with the most substituted C is the most stable. So the answers are : B and B.

thanx for the input i appreciate it, i'm sorry but i'm still not understanding it, i was wondering if you could go in a little bit more detail or sum it up easier. But i appreciate your help greatly

 

[gym.addict]

Let me see if I can help clarify. Alkyl groups are "electron donating". So for the case of having a carbocation or carbon with a radical, the more alkyl groups attached to the carbon containing the positive charge or radical, the more stable the carbon will be because the alkyl groups "donate" its electron density to that carbon thereby making it "less positive" or "less radical" and therefore more stable. I believe its called hyperconjugation. So, a tertiary carbocation is more stable than a secondary carbocation which is more stable than a primary carbocation (3>2>1), and the same goes for carbons with radicals. The opposite is true with carbanions, here, alkyl groups destabilize the negative charge because the alkyl groups would push electron density towards the negative charge and making it more negative and therefore less stable. So for carbanions, a primary carbanion is more stable than secondary which is more stable than a tertiary. I hope this helped you out, at least a little? If not, sorry 😀