Jul 8, 2016
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Pre-Medical
I know that with internal alkynes, H2, and Lindlar's catalyst, you can reduce the alkyne to an alkene without worrying about it being totally reduced to an alkane. However, I also know that alkynes are less reactive than alkenes. Why would an alkyne react with H2 and Lindlar's catalyst, but not an alkene (that was an alkyne before, but was reduced to an alkene)?
 

bobeanie95

2+ Year Member
Apr 19, 2016
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Pre-Medical
Alkynes are inherently less reactive than alkenes because they form a vinylic carbocation upon nucleophilic attack. However, it's not the reactivity of the alkyl chain that determines the reduction. Rather, Lindlars is used because it is a modified metal that only allows one level of reduction. So if you were to reduce an alkyne with excess H2 and Lindlar, you'd get an alkene, simply because of the way Lindlar's was designed. On the other hand, reduction of an alkyne using excess H2 along with a palladium catalyst will allow full reduction to an alkene.
 
OP
Q
Jul 8, 2016
6
0
Status
Pre-Medical
Alkynes are inherently less reactive than alkenes because they form a vinylic carbocation upon nucleophilic attack. However, it's not the reactivity of the alkyl chain that determines the reduction. Rather, Lindlars is used because it is a modified metal that only allows one level of reduction. So if you were to reduce an alkyne with excess H2 and Lindlar, you'd get an alkene, simply because of the way Lindlar's was designed. On the other hand, reduction of an alkyne using excess H2 along with a palladium catalyst will allow full reduction to an alkene.
Thank you so much!
 

BerkReviewTeach

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May 25, 2007
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Why are you asking this? It is not tested on the MCAT. It hasn't been tested in years. If you are using materials that contain that for your review, they are likely outdated.
 
Jul 30, 2016
177
36
Status
Pre-Medical
I know that with internal alkynes, H2, and Lindlar's catalyst, you can reduce the alkyne to an alkene without worrying about it being totally reduced to an alkane. However, I also know that alkynes are less reactive than alkenes. Why would an alkyne react with H2 and Lindlar's catalyst, but not an alkene (that was an alkyne before, but was reduced to an alkene)?
I thought there was no alkene or alkyne chemistry on the exam. Am I missing something?