Organic Chemistry Chapter 6 Part 1

WHat is an alkyl

any carbon hydrogen chain

WHat does a C-halogen bond allow for?

a partial positive charge to be on the carbon, resulting in it to be attacked by a nucleophile.

What is a methyl halide?

halogen bonded with a methyl group (0 carbons attached to the main carbon that the halide is bonded to)

What is a primary halide?

1 carbon attached to the main carbon that the halide is bonded to.

What is a secondary halide?

2 carbons attached to the main carbon that the halide is bonded to.

What is a tertiary halide

3 carbons attached to the main carbon that the halide is bonded to.

What is a geminal dihalide?

2 halogen atoms are bonded to the same carbon

What is a vinemal dihalide?

2 halogen atoms are bonded to adjacent carbons

What happens in the SN2 reaction?

the halogen atom on the alkyl halide is repleaced with the nucleophile. Since the halogen is more electronegative than carbon, the C-halogen bond breaks, and the halogen leaves, stealing the electrons in the bonded pair.

What are the qualities of a good nucleophile?

1. very electronegative

2. lots of lone pairs. 

what is a concerted reaction

new bond forming and old bond breaking at the same time

What is the order of the SN2 reaction?

second orderq

What does rate = for SN2?

Rate=k[alkyl halide][nucleophile]

Why does SN2 prefer a strong nucleophile?

because the rate of the reaction depends on the nucleophile

How many steps are in SN2?

1

Is SN2 endo or exo thermic?

exothermic

What factors determine how SN2 occurs?

1. strength of nucleophile

2. Solvent effects with nucleophile

3. Leaving Group ability

4. Structure of Substrate

How does strength work with nucleophiles?

stronger nucleophiles react faster

strong bases are strong nucleophiles, but not all strong nucleophiles are basic

Strength is based on larger radius

What do the solvent effects do with the SN2 reaction?

polar protic solutions have acidic hydrogens (OH or NH) that can solvate the nucleophile, reducing their nucleophilicity.

What types of solutions do SN2 reactions occur better in?

aprotic solvents as they lack the ability to form hydrogen bonds

What is the leaving group ability for SN2?

The best leaving groups are

electron-withdrawing to polarize the carbon atom

stable (not a strong base) once they have left

Polarizable (to stabilize the transition state)

What are the weak bases and ions that are common leaving groups?

ions: halides, sulfonate, sulfate, phosphate

neutral molecules: water, alcohols, amines, sulfides, phosphines

Why are bases not good leaving groups?

they will try to grab hydrogen groups

What does the structure of the substrate for SN2 reactions determine?

the rate of the reaction

CH3>1>2>3. 

Are tertiary halides highly reactive in SN2?

no, the reaction does not occur

What are some good nucleophiles for SN2

I, OH, OR, SH, SR, NH3, (CH3CH2)3P, (CH3CH2)2NH, CN, OH, CH3O

What happens to the configuration after an SN2 reaction?

it is inverted (walden inversion)

Why, in SN2, do the carbon attack the opposite side of the carbon from where the halogen is?

that is where the partial positive charge from the electronegativity difference is present.