MULTIPLE? hydride shifts in electophilic addition reaction

[Dentalicous1234]

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H2C=CHCH(CH3)2 + HBr ----> H3CBrCHCH(CH3)2
(electophilic addition reaction)

it says that's the major product but woudln't you do hydride shifts and get the + to be all the way over close to the more substituted carbons?

When doing hydride shifts can you just only move over one? i think you can move more than once...like here you can move from end to other end of the molecule to get to the more substitued C?

 

[chessxwizard]

In this case, you would not do a hydride shift because the positive charge lies on a secondary carbocation. A hydride shift cannot make a more stable carbocation.

If you had CH2=CH-CH-(CH3)2, and added HBr, it would do a hydride shift because it would transfer the positive charge from a 2* to a 3* carbocation, which is more stable. Hope this helps.

 

[DailyDrivenTJ]

Isn't that simple addition of hydrogen halide into alkene following the rule of the Markovnikov's rule?

 

[Dentalicous1234]

In this case, you would not do a hydride shift because the positive charge lies on a secondary carbocation. A hydride shift cannot make a more stable carbocation.

If you had CH2=CH-CH-(CH3)2, and added HBr, it would do a hydride shift because it would transfer the positive charge from a 2* to a 3* carbocation, which is more stable. Hope this helps.

thanks for the response but yea that's the molecule i was trying to depict...exactly it would shift to the more substitued 3* Carbon. isn't what I drew and what you drew the same? How come on achiever test it shows that the major product does NOT shift?

The reaction condition show HBr at 0 degrees Celsius...does it have something to do with the temp? like at this temp we dont' do hydride shifts for this EAS?

 

[chessxwizard]

Hm... oops about the structure. It's been a long day. 🙂

It might be because of the temperature, but I think temperature only matters when you are doing addition to dienes and such, when there's a thermal and kinetic product. Also, temperature matters when doing substitution/elimination and diels-alder. Can someone weigh in on this issue?

Which achiever test was this on?

 

[Dentalicous1234]

Hm... oops about the structure. It's been a long day. 🙂

It might be because of the temperature, but I think temperature only matters when you are doing addition to dienes and such, when there's a thermal and kinetic product. Also, temperature matters when doing substitution/elimination and diels-alder. Can someone weigh in on this issue?

Which achiever test was this on?

i think it's number 96...on test 1 or 2.

 

[predentn]

i think it's number 96...on test 1 or 2.

Test 1. Maybe you have a different version of Achiever than I do but the answer is indeed the tertiary alkyl bromide.

 

[chessxwizard]

Yup, indeed it is. The tertiary alkyl halide will form. You might want to check if you have the latest version of Achiever. 👍