Chem Final

Question 1

Substitution Reactions With Alkyl Halides

Answer 1

-when treated with a nucleophile, the nucleophile will replace the halogen on the alkyl and the halogen will become a product on its own

Question 2

Elimination Reactions With Alkyl Halides

Answer 2

-when treated with a base, a pi bond will be formed, a hydrogen removed due to the pi bond bonding to the base and the halide being a product on its own

Question 3

The Function of Halogens for Substitution and Elimination Rxns

Answer 3

-The halogen withdraws electron density via induction, rendering the adjacent carbon atom electrophillic and therefore subject to attack by a nucleophile (nucleophile replaces where the halogen was bound so that the carbon can take its lone electrons since it was left slightly positive from the halogen)

-the halogen can serve as a leaving group, and substitution/elimination processes can only occur when a leaving group is present (good ones are the conjugate bases of strong acids and are weak bases)

Question 4

Structure of Alkyl Halides

Answer 4

-the alpha positioned carbon is directly connected to the halogen (only one)
-beta carbon position are the carbons connected to the alpha (can have up to 3)
-alkyl halides are classified as primary, secondary or tertiary based on how many alkyl groups are attached to the alpha carbon

Question 5

Substrate

Answer 5

= alkyl halide

Question 6

Concerted Mechanism

Answer 6

-loss of the leaving group and nucleophile replacing the halogen occurs at the same time

Question 7

Step wise mechanism

Answer 7

loss of the leaving halogen group (creating a carbocation) and then the nucleophile attacks and attaches on to replace where the halogen was (bonds to change the carbocation)

Question 8

SN2 Reactions

Answer 8

=substitution, nucleophilic, bimolecular (alkyl halide and nucleophile must collide with each other)
-the nucleophile attacks the alkyl halide (substrate) from the back side which then changes the configuration of the overall molecule to the opposite when the leaving group is removed and the nucleophile is attached

-methyl alkyl halide > primary alkyl halide > secondary alkyl halide (decreasing reactivity)
-tertiary one = no reactivity (too many beta substituents)

-aprotic solvents (without the H+ attached) and solvents with charges on them are best for SN2 reactions

Question 9

E2 Reactions

Answer 9

-uses a base to attack a hydrogen on the beta carbon and then the halogen is the leaving group with the H bonded to the base)
-can occur on tertiary substrates since the base is not attacking the alpha carbon

Question 10

Alkene Isomerism

Answer 10

-assigning E to Z on alkenes … (similar to R or S configuration)

-more alkyl groups = more stable alkene

-trans = more

Question 11

water is a weak nucleophile