Sn1, Sn2, E1, E2 reactions

Why do Sn2 reactions require a good leaving group?

Because a good leaving group will readily leave from the substrate so the reaction can take place and is stable enough with its negative charge to not be reactive and bind the substrate right after leaving, allowing the nucleophile to attack (weak bases are best ex: Cl, Br)

Why do Sn2 reactions require a good nucleophile?

Because good nucleophiles have a full blown negative charge, meaning it will be very reactive and want to quickly attack the positive nuclei of the targeted carbon atom, allowing the Sn2 reaction to occur in one step (conjugate bases are best ex: OH-, NH2-)

Why do Sn2 reactions require back side attack?

Because since these reactions require good nucleophiles and good leaving groups which are both electron-rich, if front side attacked occurred it would create electron-electron repulsion, which is unfavorable

Why do Sn2 reactions require an unhindered substrates?

Because Sn2 reactions require back side attack, which is easiest to accomplish on a molecule that does not have a lot of steric crowding (primary carbons are best)

Why do Sn2 reactions prefer polar aprotic solvents?

Because nucleophiles will not be solvated in these solvents, meaning regardless of size, any nucleophile can attack faster because they do not have to break a “cage” when surrounded by solvent molecules

Why do Sn1 reactions require a weak nucleophile?

Because a good nucleophile would attack the targeted carbon atom right away and in Sn1 reactions there needs to be time allotted for the carbocation to form in the rate determining step

Why do Sn1 reactions require a good leaving group?

Because a good leaving group will readily leave from the substrate so the reaction can take place and is stable enough with its negative charge to not be reactive and bind the substrate right after leaving, allowing the carbocation to form (weak bases are best ex: Cl, Br)

Why do Sn1 reactions require a hindered substrate?

Because hindered substrates form more stable carbocations because tertiary carbons have more alkyl groups attached that can diffuse the electron density of the +1 charge across more carbon-hydrogen bonds

Why do Sn1 reactions prefer polar protic solvents?

Because in polar protic solvents the leaving group can be solvated and prevented from reacting with the carbocation again, promoting the attack of the nucleophile