Organic Chemistry Resource- Week 8

Hi everyone! I hope y’all are doing well. This week most classes are going over chapter 7, which is all about substitution reactions. This is a dense and very important chapter so get lots of practice in. Don’t forget that group tutoring is every Tuesday at 5:30 PM! Here is the link to sign up https://www.baylor.edu/support_programs/index.php?id=40917

Key Terms: Substitution Reaction, nucleophile, electrophile, nucleophilic attack, Loss of leaving group, SN1, SN2

Arrow pushing and carbocation stability: a review from chapter 6:

• Here are some awesome videos for arrow pushing and carbocation stability o https://www.youtube.com/watch?v=WaHRfIsi-SU&feature=youtu.be o https://www.youtube.com/watch?v=9aCHv67i4tM&feature=emb_title

Substitution reaction overview: • What is a substitution reaction? It is the substitution of one group for another o Ex:

• Every substitution reaction has 2 Core steps that happen o Loss of leaving group o Nucleophilic attack • SN1 and SN2 reactions are the 2 types of substitution reactions, but they have different ways of carrying out the core steps o SN1: loses leaving group 1st, then the nucleophile can attack. This is a sequential process o SN2: nucleophilic attack and loss of leaving group happen at the same time. This is called a concerted process § Ex.

The SN2 Mechanism: • Here is a video to help: https://www.youtube.com/watch?v=Z_85KXnBSYc • Kinetics: o Rate=k[substrate][nucleophile] o Sterically hindered electrophiles react slower: § Primary substrates are favored for SN2 To tell if it’s primary, secondary or tertiary, look at the # of alkyl groups attached to the electrophilic carbon

Increasing rate of reaction • Stereospecifity o If the alpha carbon is chiral, the stereochemistry of the product will inverted compared to reactant o https://www.youtube.com/watch?v=QxIUeYAQRy0

• Drawing the mechanism o Nucleophilic attack and loss of leaving group happens at the same time o Ex.

Don’t forget that strong acids, strong bases, and salts completely dissociate in solution. When this happens, only the anion is the nucleophile

The SN1 Mechanism: • Video!! https://www.youtube.com/watch?v=eB5NVPzBCzM • Kinetics: k=[electrophile] o Tertiary substrates are favored § Ex.

Increasing rate of reaction

• Stereochemistry o https://www.youtube.com/watch?v=jUEzjS0IFxs

• Drawing the mechanism o Core steps in bold purple, other steps may or may not happen § Proton transfer (usually if leaving group is a hydroxyl group) § Loss of leaving group § Carbocation rearrangement § Nucleophilic attack § Proton transfer Ex:

1. Hydroxide is a bad leaving group so it must be protonated before it can leave

3. Nucleophilic attack

2. Leaving group leaves

Practice: draw the full mechanism for the following

Answers:

2. Methyl shift to put carbocation on 1. Leaving group leaves more stable position 3. Nucleophilic attack

4. Proton transfer to get rid of positive charge on oxygen

1. Nucleophilic attack and loss of leaving group