Halogenation of Alkenes - Reaction Mechanism for Bromination and Chlorination

[@BrezHurley]

The first brominium ion should only have 2 lone pairs, not 3.

[@Leah4sci]

You're right, the bromonium ion should only have TWO lone pairs of electrons on bromine. I've also noted it in the description. Thanks for pointing it out, I appreciate it!

[@thembelihlembayimbayi7152]

You're a remarkable tutor. Thank you very much for this lesson.

[@Leah4sci]

Thanks for the kind words. You're welcome

[@kgaugelokhosa1479]

A FRIEND TOLD ME ABOUT YOUR VIDEOS AND NOW I THANK HER AND YOU SO MUCH .... I AM KILLING ORGANIC CHEM THIS SEMESTER

[@Leah4sci]

WOOHOO!!!!

[@owo3822]

Thanks, Leah! It has been 8 years since you upload this video. It's helping me a lot. I hope you're having a great day.

[@Leah4sci]

Glad it was helpful!

[@samsonmagombazulu308]

your videos are so wonderful, i am learning a lot about these reactions

[@Leah4sci]

Awesome, thanks for watching!

[@megacitationx]

Ohhh okay. This makes more sense to me now. I was wondering why the bromine/chlorine just HAD to attach to two carbons instead of just one! Thank you so much!!!

[@Leah4sci]

Glad I could help and you're so welcome!

[@mysweetestpotato]

Thank you so much, Leah! I was having so many issues with alkene reactions and your videos have helped so much!

[@Leah4sci]

You're very welcome, happy to help!

[@hyderusmael7343]

leah, thanks a lot, you made it easy to understand and now am ready for the final exam tomorrow

[@Leah4sci]

Awesome!

[@kamatmehbro]

This was sooo good! Good speed, clear communication and amazing explanation at each step! Thank you for all that you do!

[@Leah4sci]

You're very welcome, happy to help!

[@MariRei]

Thank you for this! I understand the concept so much better when I see exactly what is happening~

[@MariRei]

***** Yes. Learning it for the first time~

[@Leah4sci]

You're welcome, so happy I can help clear the concept!

[@SagarPatel-bf2sq]

love your explanations and how to share the thought process of EVERY reaction so we cannot get confused.

[@sazalking]

***** best way to learn!

[@Leah4sci]

So glad you like it!

[@Calle895]

Your videos have been so so helpful! I can't thank you enough.

[@Leah4sci]

Aww you're so welcome!

[@alinodavinci9371]

Thank you so much , you made it easy to the understand ❤

[@Leah4sci]

You're welcome! Glad I could help!

[@skiphoffenflaven8004]

On the bromonium ion, there should only be two pairs of electrons on the bromine atom, to give a formal charge of 7-2-4 = +1. With three lone pairs, the formal charge would be 7 - 2 - 6 = -1 on the bromine atom.

[@Leah4sci]

Thank you for pointing that out! You are correct. The bromonium ion should only have two lone pairs of electrons.

[@shaifuseth5566]

Thanks a lot mam for that simplified explanation, it helped a lot

[@Leah4sci]

Glad this helped you! You're welcome! :)

[@paulringab123]

amazing. Thank you very much for this amazing explanation. You're amazing.

[@Leah4sci]

You're so very welcome!

[@paulringab123]

yes i finally got a reply!!!

[@xxxSuperStarxxxZ]

You're helping me so much thank you leah!

[@Leah4sci]

Happy to help!

[@Smiles5s5s]

Thank you so much! I never actually understood why this reaction created a cyclic bromonium ion intermediate until now!

[@Leah4sci]

you're so welcome!

[@markbinnis9777]

at 1:25 i think you mean "symmetrical" not "asymmetrical". Please correct me if I'm wrong.

[@JensengTea]

I think she does mean asymmetrical. It has the same atoms on either side of the dashed line, but they are not mirrored. But, hell... I'm taking orgo for the second time so I obviously don't know very much lol

[@IsabelHernandez-cm5bd]

I think she said “ a symmetrical” not “asymmetrical” ???

[@Leah4sci]

Oh wow, yes you're absolutely correct! Symmetrical due to having a pi bond with a methyl group on each side 🤦

[@arsenal78910]

at min 2:40, shouldnt bromine be having two lone pairs only?

[@Leah4sci]

Yes thanks for pointing that out. That was a mistake on the video but youtube does not allow editing once it's posted

[@shanebergeron1544]

this explanation of the bromonium bridge on the cyclohexane is excellent. Hope you have some stereoisomerism videos ...

[@Leah4sci]

Glad you enjoyed it!

[@c.o2307]

Last example was pefectly explained

[@Leah4sci]

Glad to hear it!

[@Iit-yg2he]

This video is awesome ❤❤ lots of love from India

[@Leah4sci]

Thank you so much

[@OrcjaEnglish]

7:10 I think , the secondary carbocation has low positive density as it is bonded to the methyl group which is electron donating group that is decreasing its positive density and making it more stable than primary carbocation. Kindly see it.

[@Leah4sci]

No, secondary carbocations are always more stable than primary carbocations. To learn more about why carbocation stability is ranked like this, make sure to read my carbocation tutorial at Leah4sci.com/carbocation

[@OrcjaEnglish]

@@Leah4sci I have also explained this one. Although, our point of concern is similar. Thanks!

[@mariaavedissian4853]

Leah, you are the best!!

[@Leah4sci]

Thanks so much!

[@mrpb506]

leah, ur awesome!!!!!!!!!!!!!!!!!!! im actually understanding this now! because ofu i just might pass my test on wed yayyyyyy :-)

[@Leah4sci]

Aww thanks! So glad I can help!

[@sameerkhnl1]

Very helpful! Thank you very much Leah.

[@Leah4sci]

you are so very welcome!

[@benwilliams1889]

Wonderfully explained

[@Leah4sci]

Glad you liked it!

[@afal5547]

you are saving my life I love you

[@Leah4sci]

Happy to help!

[@tuktak835]

Thank you very much! My online teacher 😛👍❣

[@Leah4sci]

You're welcome!

[@yuzu8284]

YOU ARE MY HERO..THANK YOU VERY MUCH..WISH YOU THE BEST

[@Leah4sci]

You're very welcome, happy to help!

[@mcvaqua]

when you drew the bronium (?) ion you should have only two lone pairs no? just wondering if I got it wrong. I really utilize these tutorials. I hope you make more doing this than a professor does. You're certainly better than some.

[@Leah4sci]

Sorry yes, that was an error. I placed a note in the description and pinned a comment. Thank you for pointing it out!

[@thamsanqafaku6942]

You saved my life, I want to cry

[@Leah4sci]

So glad this helped you!

[@jl6930]

so, the fact that a bridge forms means that the bromide anion is blocked from doing a frontal attack. thus, it can only do a backside attack on that partially positive electrophilic C. this is why the anti-positioning occurs between the two bromine atoms.

[@Leah4sci]

Exactly!

[@itzzakshay1797]

Nice video it cleared my concept

[@Leah4sci]

Glad I could help!

[@chandrakommanapotluri7306]

OMG! You are a life saver

[@Leah4sci]

So glad to save a life :)

[@bekenrenov]

That was an excellent explanation. Thank you

[@Leah4sci]

You're so welcome!

[@tamannakapoor1840]

Thank you so much for these videos, they are a lot helpful. I get stuck when it comes to their stereochemistry and number of products formed including the stereoisomers. Can you help and bring some videos on it? Thank you

[@Leah4sci]

You're so welcome! The formula for the number of stereoisomers of any given molecule is 2^n where n is the number of chiral centers in the structure. To access my free video series on Chirality and Stereochemistry, visit Leah4sci.com/Chirality For further help with topics like this and more, I recommend joining the organic chemistry study hall. Details: leah4sci.com/join or contact me through my website leah4sci.com/contact/

[@TheThorRs]

2:55 can someone provide me with an alternative explanation as to why the bromine can't bind to that carbon she said it can't bind to? I'm having a hard time seeing where this bromonium bridge might be. thank you

[@TheThorRs]

Like could you not just put the bromine there and change the wedges/dashes accordingly?

[@Leah4sci]

The explanation that I make at 2:55 is that the bromide ion cannot attack on the side of the molecule with the other bromine. It must attack on the side where there is a clear view of the carbocations. There are no wedges or dashes drawn here, meaning no stereochemistry shown. The bromonium bridge is simply the bromine that is 'bridged' by being partially bonded to both carbons. Bromide will always attack from the other side as the bromonium bridge.

[@TheMadMike8]

fuaaark, such an aesthetics tutorial. Heaps Good!!!!

[@Leah4sci]

glad you liked it!

[@dhruvyadav7138]

Wow u r still active and commenting , btw thanks for clearing my doubt

[@Leah4sci]

Yes, I love to connect with my viewers! You're welcome.

[@anastasiasoskovets9489]

Great video! Helped me to understand the mechanism a lot better. Question about the last reaction, if we were to show stereochemistry it would still be an anti addition, 1 Cl coming at us and one from behind?

[@Leah4sci]

Correct. This reaction displays anti addition.

[@dezhiliu1687]

This saved me thank you!

[@Leah4sci]

So glad it helped!

[@TheGabXD]

the bromonium ion should only have 2 pairs of electrons and not three right?

[@ghadaghonaim7879]

TheGabXD yeah , I thought the same

[@gabenir5117]

yes, she mentioned it on one of the comment

[@Leah4sci]

Yes, the bromonium ion should only have TWO lone pairs of electrons on bromine. I've also noted it in the description. Thanks for pointing it out, I appreciate it!

[@biochemacademy5608]

Very well explained

[@Leah4sci]

Glad it was helpful!

[@salmahameed4871]

Very well explained thanks

[@Leah4sci]

Glad it was helpful!

[@SwastikSwarupDas]

You are absolutely amazing thanks

[@Leah4sci]

You're welcome! and Thank you! :)

[@bhumikagupta5071]

so so good!! one doubt mam that why is in the first step,why bromine attacks back to the pi-electron?

[@Leah4sci]

Great question. Br does not like to get attacked and having those extra electrons makes it super reactive

[@bhumikagupta5071]

@@Leah4sci so mam does it happen with other halogens as well?

[@bhumikagupta5071]

@@Leah4sci so doesn't this happen with other halogens mam?

[@lauritseriksen4140]

Hey ***** :) At 2:28 you draw a positive charge to the bromine in your intermediate. But from your drawing bromine has a formal charge of -1. Don't you need to remove an electron pair? Btw your videos and i learn a lot from them :)

[@Leah4sci]

Yes, the bromonium ion should only have TWO lone pairs of electrons on bromine. I've also noted it in the description. Thanks for pointing it out, I appreciate it!

[@sudhanvab]

At 3:10 why dosent bromine attach with +ve bromine in the compound

[@Leah4sci]

I don't understand your question. The bromonium bridge is an unstable intermediate and will break open soon as the other bromine attacks carbon

[@wweuniverse9337]

hey my textbook shows ccl4 is used as a solvent,I want to know what's the role of it??

[@Leah4sci]

that's an inert solvent similar to CH2Cl2 and others

[@wweuniverse9337]

Leah4sci thanks!!

[@niloofarkh4779]

U RE THE BEST

[@Leah4sci]

Awww thanks!

[@paburax]

Amazing !

[@thyronorm]

Bhai tera kuch nahi ho sakta..!! Matlab har jagah padhai! XD

[@Leah4sci]

thank you!

[@asifalamjoy9530]

Leah, could you please make a video on Hybridization??

[@Leah4sci]

I'm sorry, but I don't offer tutoring through KZbin comments. For help with this and more, I recommend joining the organic chemistry study hall. Full details: leah4sci.com/join

[@thejetsonslol]

Good explanation. Is there steriochem?

[@Leah4sci]

Do you mean videos? Have you seen this series? leah4sci.com/chirality-stereochemistry-enantiomers-diastereomers-r-s-organic-chemistry-tutorial-series/

[@sharonsoh3027]

hi, may i know what is the purpose of diether ethyl added to the bromine for alkane and alkene to undergo substitution or addition reaction?

[@Leah4sci]

I'm sorry, but I don't offer tutoring over social media. If you ever find you need help with questions like this again, I recommend joining the organic chemistry study hall. Details: leah4sci.com/join or contact me through my website leah4sci.com/contact/

[@karabelomaghalemela9576]

Thank you so much for this

[@Leah4sci]

You're very welcome!

[@hanajb8317]

sorry but i have a question ::: the first br when attached with both c

[@Leah4sci]

Yes that was a mistake. The bromonium ion should only have TWO lone pairs of electrons on bromine. I've also noted it in the description. Thanks for pointing it out, I appreciate it!

[@manijas4807]

How do you know whether to draw the final product out w/ a wedge/dash/ or flat line?

[@Leah4sci]

Both show the same molecule, but in a different way, so it depends on the question. The question will ask you to show your answer in a specific format. If not, then ask your professor which one he/she prefers

[@sureshkumarlamror5119]

Good explanation

[@Leah4sci]

glad you liked it

[@celesteadeanes4478]

Is there such a thing as a survey of the reagents and there uses on your playlist? I'm overwhelmed with most of them except bromine cause its simplest .

[@celesteadeanes4478]

Maybe a wheel chart

[@Leah4sci]

Something for me to consider

[@suvankarbanerjee6048]

In 2 degree delta positive carbon There Is steric hindrance then why cl would attack

[@TCToni]

I was thinking this as well

[@VndNvwYvvSvv]

Imagine the stereochemistry. for example, with the Cl bridge away from us in the plane of the drawing, the #3 carbon in the plane of the drawing, this leaves the carbonation toward us, trigonal planar and sp2 hybridised, which is trans to the bridge. Unless I'm mistaken, this leaves little stearic hindrance.

[@Leah4sci]

This is a very good question and slightly tricky concept. The bridged intermediate appears to undergo an SN2 reaction, however because of the ring strain, the ring itself causes the molecule to change shape slightly (vs a standard sp3 hindered carbon) along with the charged/partially charged unstable intermediate together making it accessible enough for the backside attack

[@Leon-tq2dd]

Thank you so much! No one explained that it was the resonance structure that contributes the bridge formation. Everything makes sense now.

[@Leah4sci]

So happy to clear things up for you!

[@v2385-u2n]

could u please give the video of epoxidation of cholesterol???

[@Leah4sci]

I have no plans to cover this topic at this time. This channel is focused on undergraduate level organic chemistry and this topic is beyond that scope.

[@renoyking7828]

i got it thnks sooo much BTW thats a nice voice

[@Leah4sci]

Thanks so much!

[@Nic01a]

Thank you for this

[@Leah4sci]

My pleasure!

[@ArianaKhan-bp4qs]

1:15 why Br is attacking back.

[@Leah4sci]

Br is an electronegative atom, when the pi bond attacks, the carbon no longer holding the pi bond is now left deficient and therefor positive. The electronegative Br is attracted to it and therefor attacks

[@ArianaKhan-bp4qs]

@@Leah4sci Thank you..

[@kimwiyual2396]

L9ve your beautiful brain Leah. Happy New year

[@Leah4sci]

Thank you so much! Happy New Year to you too!

[@Muhammadshoaib-ow1km]

soo helpful mam thanks a lot

[@Leah4sci]

Glad the video helped! You're welcome! All the best!

[@flungoutofspace9]

at 2:41, there should be only 2 lone pairs on bromine instead of three. otherwise, great video :D

[@michaelpa1110]

I don’t think so because this is a resonance structure where one electron pair is from bromine is attacking 2 carbons, back and forth!

[@Leah4sci]

Yes, you're right! Thanks for pointing it out. It's noted in the description and a pinned comment now.

[@preciousdaisy1234]

Thank you for the video

[@Leah4sci]

You are very welcome!

[@MysticMD]

Thank you sosososo much!!!

[@Leah4sci]

You are very welcome!

[@Teenageriot280]

i love you for this

[@Leah4sci]

happy to help!

[@TheRayanKhan]

Why the secondary carbon becomes more positive then the primary carbon in Chlorination?

[@Leah4sci]

At which point in the video?

[@alexayala9843]

Is the bromonium ion always an intermediate step?

[@Leah4sci]

For this reaction, yes

[@haydentweedy9067]

Is it necessary for the Alkene to be gaseous

[@Leah4sci]

I'm sorry, but I don't offer tutoring over social media. If you find you still need help with questions like this, I recommend joining the organic chemistry study hall. Details: leah4sci.com/join or contact me through my website leah4sci.com/contact/

[@VndNvwYvvSvv]

Wouldn't you have to say that the electrophilic reaction to the more stable carbonation leads to the major product and the other is the minor rather than stating it's just THE product?

[@Leah4sci]

I think technically you are correct, however the percentages as determined in laboratories are so extreme that in this case you can disregard the minor product

[@kamohelolesofe7670]

thank you so much

[@Leah4sci]

You're very welcome!

[@mohmedbadr1947]

is there a reaction to add X2 syn addtion

[@Leah4sci]

Yes but it's a trick. Start with a cis alkene then flip. Try this with your model kit

[@ItsKirstyGreene]

Will halogenation of alkenes always result in trans molecules?

[@Leah4sci]

cis/trans refers to pi bonds. If the bond is broken there’s no cis/trans. The resulting dihalide can rotate allowing the halogens to be together or apart. What you have to pay attention to instead is the anti addition (here) vs syn addition in other reactions.

[@adiga202]

oh right, got it. thanks leah ! ^_^

[@Leah4sci]

you're welcome!

[@therightway1205]

Excellent

[@Leah4sci]

glad you like it!

[@shouryaa3388]

So basically rearrangement of C+ wont occur //???

[@Leah4sci]

Correct, because it is not a distinct carbocation intermediate that is formed in this reaction. Rather, it is a halonium bridged intermediate. For help with questions like this and more, I recommend joining the organic chemistry study hall. Details: leah4sci.com/join or contact me through my website leah4sci.com/contact/

[@shouryaa3388]

@@Leah4sci thnq mam (✿◠‿◠)

[@soumyadip3751]

thank you so much :)

[@Leah4sci]

You're welcome!

[@rouwani]

thanks for this

[@Leah4sci]

you're welcome

[@claricea5353]

THANK YOU

[@Leah4sci]

You're welcome!

[@davidmgooden8320]

your mechanism is incorrect. Br2 additions do not go through carbocations.

[@Leah4sci]

Which part of the video? (timestamp please)

[@davidmgooden8320]

Leah4sci at 1:21 you correctly show three arrows which should take you straight to the bromonium. You eventually get there but you mention and show discrete carbocations starting at 1:38. Also the alkene is not asymmetrical as you state. After 1:38 the arrow showing the Br moving to the adjacent cabin is correct but the resulting cation isn’t. The only way to put a positive charge on that carbon is to break the C-Br bond. Your arrow shows attack of Br valence electrons on a carbocation not a Br migrating.

[@youknowwhere6890]

Awesome

[@Leah4sci]

Thanks! :)

[@varindersinghkainth5026]

thanku from varinder singh specaily

[@Leah4sci]

you're welcome!

[@manarmohammed7974]

How is it trans of the cyclohexane the bromine atoms are on the same side so its a cis not a trans

[@Leah4sci]

When looking at cyclic molecules, cis means both are on wedges (up) OR both on dashes (down). For trans you'd have one up and one down. Halogenation of a cycloalkene yields a trans product where one is up and the other down

[@racpatrice]

***** Thank you soooo much for your videos, I'm understanding this material so much better now :)

[@Leah4sci]

You're very welcome!

[@prempatil7623]

who exactly are those 12 people who disliked it????????

[@Leah4sci]

Good question!

[@yadpreetcheema4806]

Great explanation, now instead of memorizing they are trans , I understand why and won't forget.

[@Leah4sci]

Thank you. Glad the video helped/

[@Hamza2436]

nice nice

[@Leah4sci]

thanks!

[@SalmanAli-e8u5k]

Hey mam how are you?

[@Leah4sci]

Good, thanks