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Topic: Reaction with Excess H2/Pd? This is kind of confusing!  (Read 9788 times)

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Offline webassignbuddy

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Reaction with Excess H2/Pd? This is kind of confusing!
« on: September 18, 2013, 09:18:52 AM »


For the bottom reaction, wouldn't the product be this (when the C=C double bond on the far right breaks as 2 electrons from it get pushed onto the top carbon, which then attacks the H-H and the H nucleophile attacks the electrophilic carbon):

CC2=C(c1ccccc1)CCCCC2

For the IUPAC I wrote, cis- 1-methyl-2-phenylcyclohept-1-ene (ene for the double bond at 1!) But that's wrong :(

The answer is supposed to be cis-1-methyl-2-phenylcycloheptane

I don't understand :(
1) Do BOTH C=C double bonds in cycloheptane get reduced to CH-CH because it's EXCESS H2/Pd? Also did I describe the Excess H2/Pd mechanism correctly?
2) Does the correct answer look like this?

CC1CCCCCC1c2ccccc2

3) Why wouldn't I reduce all the double bonds in the benzene? Is it because H2/Pd catalyst in general can't because it's not a strong enough reagent and it's only used for alkenes?

4) How exactly do you name a structure like this? I know that cis means 2 things are on the SAME side of a bond (hence on the far right of the cycloheptane structure, the H's are sticking OUT on the same side of the C-C bond because there's a lot of space/elbow room, and on the top left of the cyclheptane structure, the H's would be sticking INTO the page while being on the same side of the C-C bond because it's crowded). Is my reasoning correct?

Offline discodermolide

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Re: Reaction with Excess H2/Pd? This is kind of confusing!
« Reply #1 on: September 18, 2013, 09:28:38 AM »
I variability hydrogenation of such double bonds gives the cis product. Imagine the molecule approaching the catalyst surface. It can only do so when both substituents point up out of the plane. This gives the cis product.
Reduction of the aromatic ring requires either special catalysts or pressure and temperature.
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Offline webassignbuddy

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Re: Reaction with Excess H2/Pd? This is kind of confusing!
« Reply #2 on: September 18, 2013, 09:36:38 AM »
I variability hydrogenation of such double bonds gives the cis product. Imagine the molecule approaching the catalyst surface. It can only do so when both substituents point up out of the plane. This gives the cis product.
Reduction of the aromatic ring requires either special catalysts or pressure and temperature.

What do you mean by "I variability hydrogenation of such double bonds" though?

Also, why would the top reaction in the picture below not be called cis-1,3-diphenylheptane

The correct answer is supposed to be just 1,3-diphenylheptane.
I don't understand :( You only put CIS or TRANS if there is a CYCLIC structure containing C=C double bonds??

Offline discodermolide

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Re: Reaction with Excess H2/Pd? This is kind of confusing!
« Reply #3 on: September 18, 2013, 09:47:46 AM »
Sorry the spell checker changed it.
It should be invariably.
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Offline webassignbuddy

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Re: Reaction with Excess H2/Pd? This is kind of confusing!
« Reply #4 on: September 18, 2013, 09:58:17 AM »
Sorry the spell checker changed it.
It should be invariably.

Ok so if there was just 1 C=C double bond in cyclopentane, would it still be cis?
Also do you only put cis or trans if there is a cyclic structure containing C=C double bonds??

Offline discodermolide

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Re: Reaction with Excess H2/Pd? This is kind of confusing!
« Reply #5 on: September 18, 2013, 10:03:30 AM »
In cyclopentene the double bond is cis by default.
You also use cis and trans in non cyclic structures.
In the case of the top reaction you probably get mixtures after the hydrogenation, mostly trans and some cis. So then you don't define it as cis or trans.
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Offline webassignbuddy

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Re: Reaction with Excess H2/Pd? This is kind of confusing!
« Reply #6 on: September 18, 2013, 10:05:46 AM »
In cyclopentene the double bond is cis by default.
You also use cis and trans in non cyclic structures.
In the case of the top reaction you probably get mixtures after the hydrogenation, mostly trans and some cis. So then you don't define it as cis or trans.

Hm...ok, I think I understand
Thanks

Offline webassignbuddy

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Re: Reaction with Excess H2/Pd? This is kind of confusing!
« Reply #7 on: September 18, 2013, 10:16:19 AM »
In cyclopentene the double bond is cis by default.
You also use cis and trans in non cyclic structures.
In the case of the top reaction you probably get mixtures after the hydrogenation, mostly trans and some cis. So then you don't define it as cis or trans.

For the second reaction, the answer is

4-chloro-4-methyl-1,7-diphenylheptane. But My question is, for the HCl reaction at the bottom of the diagram I posted above your most recent post is why does the Chlorine attack the most substituted carbon at 4? Why not carbon 5 on top?

Offline discodermolide

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Re: Reaction with Excess H2/Pd? This is kind of confusing!
« Reply #8 on: September 18, 2013, 10:24:29 AM »
protonation of the double bond will produce the most stable carbonic ion, that then is substituted by Cl.
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Offline webassignbuddy

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Re: Reaction with Excess H2/Pd? This is kind of confusing!
« Reply #9 on: September 18, 2013, 11:18:46 AM »
protonation of the double bond will produce the most stable carbonic ion, that then is substituted by Cl.

oh ok...so the most substituted carbon

Offline discodermolide

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Re: Reaction with Excess H2/Pd? This is kind of confusing!
« Reply #10 on: September 18, 2013, 11:29:03 AM »
Sorry about the spell checker, it should be carbonium ion. :'(
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Offline antimatter101

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Re: Reaction with Excess H2/Pd? This is kind of confusing!
« Reply #11 on: September 21, 2013, 02:07:21 AM »
That's interesting - my organic chemistry textbook says 'carbocation' instead.

Also, H3C- is spelt as 'carbanion'.

Offline hinhthoi

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Re: Reaction with Excess H2/Pd? This is kind of confusing!
« Reply #12 on: September 24, 2013, 02:15:52 AM »
carbanion and carbonium ion are the same thing

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Re: Reaction with Excess H2/Pd? This is kind of confusing!
« Reply #13 on: September 24, 2013, 04:27:28 AM »
carbanion and carbonium ion are the same thing

Just to clarify a carbanion is a carbon bearing a negative charge, usually stabilized by resonance, but it does not have to be.
A carbonium ion is a carbon bearing a positive charge resonance stabilised.
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Offline IA_khim

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Re: Reaction with Excess H2/Pd? This is kind of confusing!
« Reply #14 on: September 25, 2013, 05:21:52 PM »
To clarify even further (for those who really cares). Here are the definitions from Anslyn&Doughergy, Phys. Org. Chem., p. 52: "Carbocation" - a structure with a positive charge on a carbon atom. There are two types of carbocations - "carbenium ions" and  "carbonium ions". Carbenium ions are trivalent species (of CH3+ type). Carbonium ions include structures with three center - two electron bonding (i.e., CH5+, non-classic cations, bridged ethyl cation etc).

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