Organic Chemistry Q: SN1 SN2 E1 E2

[gotquestions]

I am having a hard time understanding this. Can someone explain it to me?

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[wes011]

Here are the basics.

SN2 and E2 reactions occur in one step. As the leaving group exits the molecule, the nucleophile attaches to the molecule. What you typically see is backside attack for SN2 molecules meaning you have inversion of stereochemistry or the nucleophile attaches to the side opposite of the leaving group. You typically see SN2 and E2 reactions occur in molecules that are not sterically hindered. For example, if you have a t-butyl group blocking the backside it is very hard for the nucleophile to attack the nucleous this way.

E1 and SN1 reactions occur in a two-step process, via a carbo cation formation. In these reactions, the leaving group leaves first and you have a carbon atom with a positve charge on it (the leaving group stole the electrons). So the nucleophile will attack the C+ ion. When looking at the SN1 product, you will notice there is retention of starting product and the inversion of product (if these are equal it is a racemic mixture). The reason why this occurs is because after the carbocation ion forms, the nucleophile can attack from either side of the positive charge easily so it is a coin flip.

If you have to distinguish between SN2 or SN1 reactions or E2 and E1 reactions you should look at the compound. If it is sterically hindered it probably goes via SN1 or E1. If it isn't sterically hindered and you have inversion of stereochemistry it is an SN2 or E2 reaction.

If you have rearrangement, this occurs only in SN1 or E1 reaction mechanisms, so that is the big tip off. You will have rearrangement of the carbocation to a more sterically hindered carbon atom because the + charge is dispersed among additional carbons atoms (look at resonance structures).

The other thing to understand is when you have competing substitution vs. elimination reactions, which are typically decided based on conditions or reactants. Make sure you read on that.

 

[thephoenician88]

http://product.half.ebay.com/Organic-Chemistry-I-As-a-Second-Language_W0QQtgZinfoQQprZ57073203

go buy this book, organic chem as a second language. It's explains all those in an easy to understand way.

 

[Sparda29]

There is no way you are gonna learn Organic by reading words, you gotta actually see the pictures and videos to understand how the electrons move around.

Google some organic chem reaction animations.

 

[OChemist]

There is no way you are gonna learn Organic by reading words, you gotta actually see the pictures and videos to understand how the electrons move around.

Google some organic chem reaction animations.

he is right, try doing some sample questions, what book are you using? they give good illustrations. The book is your best friend. Are you using L.G Wade Organic Chemistry?

wes011 is right, just read the book, it describes SN2 as a back attack, and SN1 (kind of as both) showing a racemic mixture (enantiomers) depending on the chiralty and the sterogenic center.

 

[wes011]

For the stereochemistry that only happens in SN1 and SN2 reactions because you have to have a chiral carbon to denote stereochemistry.

 

[Sparda29]

Organic Chem for dummies helped me a little, but the one thing that allowed me to ace Organic was to do every single homework problem in the book.

 

[thephoenician88]

the book i posted shows the reaction and gives you words, after that it let's you fill in the blanks based on what you've learned. good book

 

[Filler]

The best way I learned was to actually work out the problems at the end of the chapter on a notebook, but I always handle orgo like I would handle any math class, by working out the problems.

 

[medicalCPA]

Organic Chemistry as a Second Language is an incredible resource to help with this subject, just like a previous poster said.

 

[Sparda29]

Organic Chemistry as a Second Language is an incredible resource to help with this subject, just like a previous poster said.

Organic Chem really is a foreign language, only way to master it is practice.

 

[fhx06]

If you are a visual learner, you can always see if you can find someone with the box set for building molecules and try to figure it out that way as well.