Reactivity

what is a nucleophile

what is an electrophile

electron pair donor, either negatively charged or neutral

electron pair acceptor positively charged or neutral

3 important ways to identify electron distribution

formal charges - indicates atoms overall charge

bond polarisation - creates partial charges across a bond

atomic orbitals - relevant to availability and distribution of electrons

what is delocalisation

occurs when electrons are spread across several atoms - affects how readily a species reacts and how stable it is after a reaction.

provides additional stability to a molecule or region of a molecule

influences electron distribution and therefore chemical reactivity

what is a leaving group

when an atom or group of atoms break away from a molecule taking the shared electrons with it.

what is a bronsted lowry acid and base

what is a lewis acid and base

bronsted acid = donates a proton

bronsted base = accepts a proton

lewis acid = accepts an electron pair

lewis base - donates an electron pair

pKa indicates what

acid strength

low pKa = stronger acid

High pKa - weaker acid

how do identify an acid in a drug molecule

Look for an atom bonded to a hydrogen that can be lost, with the resulting species being stable. This typically involves a hydrogen attached to an electronegative atom (like O or N)

Example: A hydroxyl group (-OH) can lose its proton to form an alkoxide (-O),

phenols (OH on a ring) or carboxylic acid (COOH)

how to identify a base from a drug molecule

Bases: Look for atoms with lone pairs of electrons that can accept a proton. These are typically electronegative atoms like nitrogen or oxygen.

usually amines (NH2,NH,N) Over amides

what happens in SN1 mechanism

what happens in SN2 mechanism

SN1

Leaving group departs —> carbocation intermediate forms sp² hybridised

Nucleophile attacks the carbocation —> product forms

Rate = k [substrate]

consequence: nucleophile can attack from either face of the planar carbon after it attacks you get 50% enantiomer and 50% mirror image one

equal probability —> racemic mixure

favoured by tiertiary

SN2

single step

nucleophile attacks backside of electrophillic carbon at the same time the leaving group departs

Rate = k [substrate]

Consequence: whatever shape you start with you will get the exact opposite shape

favoured by primary and then secondary

major difference between SN1 and SN2

sn2 proceeds in one step, whilst SN1 proceeds in two steps

sn2 leads to inversion of stereochemistry, SN1 leads to racemic mixtures