Reaction Mechanisms

Question 1

Define an electrophile

Answer 1

Electron deficient species that reacts by accepting (gaining) electrons to attain a full outer electron configuration. Often seen as a negatively charged Ion

Question 2

Define a nucleophile

Answer 2

Something that has electrons available for donation to electrophiles. Often seen as a positively charged ion

Question 3

Describe the process of aliphatic substitutin

Answer 3

When a functional group occurs on a SP3 hybridised carbn

The incoming species donates a pair of electrons and then the originally connected functional group detaches and leaves, hence why it is called a leaving group.

Question 4

What determines if a leaving group is good?

Answer 4

A good leaving group are those that form stable ions or neutral molecules after they leave the substrate

Question 5

Describe an elimination reaction

Answer 5

Removal of a molecule without them being replaced by other atoms or groups

Question 6

Define a unimlecular nucleophilic substitution reaction (Sn1) and describe the rate of reaction using a formula

Answer 6

Replacement of leaving group via a nucleophile.

There is a rate determining step that determines what happens next.

Then the nucelophile attacks the carbocation from above or below

The rate is dependent upon the concentration of the substrate therefor

Rate = Rate constant multiplied by concentration of the substrate.

Question 7

What must be present for Sn1 reactions to occur

Answer 7

good leaving group

structure which the positively charged carbon is stabilized often by having it on a tertiary position

Question 8

What is a Biomolecular Nucleophillic substitution reaction Sn2

Answer 8

Single step process in which nucleophile attacks and the leaving group detachment occurs simultaneously

Question 9

Describe the rate of reaction of a sn2 reaction using a formula

Answer 9

rate of reaction dependent on both the concentration of the alkyl substrate and the nucleophile hence

Rate = Rate constant x [ substrate] x [nucleophile]

Question 10

Describe what sn1 reactions effect

Answer 10

A unimolecular nucleophillic reaction can effect
the nature f the nucleophile,

the leaving group

nature of the solvent

Question 11

Describe the level of stability of a carbocation and why Sn1 form more stable carbocations

Answer 11

The order of carbocation stability is catagorized into primary, secondary and tertiary with tertiary being dubbed the most stable

Sn1 reaction are more likely to form tertiary carbocations

Question 12

Describe how a Sn2 reaction is affected by the strength of a nucleophile

Answer 12

The stronger the nucleophile the more the reaction will be promoted as the nucleophilicity is influenced by the size of the attacking atom in the nucleophile

Question 13

name 4 things that influences the ability of a potential leaving group

Answer 13

Strength of the R Y bond

The polarisability f the bond

The stability of the leaving group

The degree of stabilisation through solvation for either sn1 or sn2 reactions

Question 14

describe how polarity of solvent effects sn1 and sn2 reaction

Answer 14

In Sn1 reaction polar solvent favour formation of the carbocation and hence favour the Sn1 reaction

In Sn2 reactions the nucleophile is involved in the rds but the nucleophile can be solvated by polar protic solvents which reduces nucleophilicity so APOLAR solvents are used to dissolve the ionic nucleophiles

Question 15

describe the term configurational isomers

Answer 15

conformational isomerism is a form of stereoisomerism in which the isomers can be interconverted just by rotations about formally single bonds.