Alkylaldhides Sn2 reactions Flashcards
Alkyl Halides (or halo-alkanes) Outline
An alkane where 1 H is replaced by a halogen eg 3 bromohexane (same nomenclature as standard alkanes)
Alpha Carbon Outline
Carbon that has the halogen attached
Primary Akyl Halides Outline
Alpha carbon with 1 extra carbon replaced
Secondary Akyl Halides Outline
Alpha carbon with 2 extra carbons replaced
Tertiary Akyl Halides Outline
Alpha carbon with 3 extra carbons replaced
What happens between the alpha carbon and the halogen to allow nucleophilic substitution
Polarisation. Carbon = delta positive. Halogen = delta negative
2 ways nucleophiles present
Negatively charged ion (atom with an extra electron) or a neutral atom with a lone pair of electrons. Typically nucleophiles are stronger if they have a negative charge
Carbon Nucleophiles Outline
Terminal Alkynes are weak acids and quite unstable
Why are halogens such good leaving groups
During polarisation they become strongly electronegative (attracts electrons strongly). This electronegativity makes the halogen very independently stable making the bond between them and the carbon weaker and making them less likely to try and reform the bond with the carbon
What does Sn2 Mean
The rate determining step (slowest step of substitution) is dependent on 2 different molecules. It is dependent on both the nucleophile and the leaving group (eg halogen)
Can you isolate the transition state ion from Sn2 reactions
No (as indicated by square brackets). Reaction is too quick (as intermediate is very unstable)
What determines the rate of the rate determining step
faster step = smaller activation energy = more electronegative the leaving group + stronger nucleophile
What happens to the chirality of a molecule that undergoes Sn2
Guaranteed inversion of configuration. (R -> S or S -> R)
What type of alkyl Halides undergo Sn2 reactions
Primary (more reactive as more space for nucleophile to attach and more electronegative leaving groups) and some secondary
