Question

1) Compare and contrast SN1, SN2, E1, and E2 reactions! (similarities abd differences. Requirements for each to work.)

2) Why is SN2 is in direct competition with E2 while SN1 is direct competition with E1 reaction.

3) Rate expression of each

4) which reactions are concerted? Which are atep wise?

5) which are sterospecific and what stereospecificity of each are?

6) how do the variables below (A-D) influence reaction pathway?

Compare and contrast SNI, SN2, El and E2 reactions. What are some obvious similarities and differences between each reaction pathway? What are the requirements for each reaction to work? Discuss why SN2 is in direct competition with E2 while SNL is in direct competition with the El reaction pathway. What is the rate expression for each? Which reactions are concerted? Which reactions are step-wise? Which reactions are stereospecific and what is the stereospecificity of each that are? How do the variables below help influence which reaction pathway will lead to the major product formed? a. Substrate (substitution pattern and leaving group ability) b. Nucleophile/base strength (weak or strong and size (unhindered or hindered) c. Solvent (polar-aprotic or polar-protic) d. Temperature (low/ambient temps vs. higher temps)

Answer 1

SN1 and E1 are two step reaction where first step is formation of carbocation. Both goes with non basic nucleophile. Both should have great leaving group so that carbocation may form easily. Both are favored by polar protic solvent as they stabilize carbocation formed in first step. In SN1 nucleophile attacks carbocation to form substitution product while in E1 base removes beta proton to give elimination product.

SN2 and E2 both follows concerted mechanism. Both are favored in polar aprotic solvent due to solvatiin of cation of nucleophile. In SN2 non basic strong nucleophile attacks to give substituted product while in E2 strong basic nucleophile gives E2 elimination.

Rate expression;

SN1, r=K[R] first order

E1, r=K[R] first order

SN2, r= K[R][Nu] second order

E2, r= K[R][Nu] second order

Stereochemistry;

SN1 gives racemic mixture . SN 2 gives inverted product so it is stereospecific. E 1 is not stereospecific as no need of antiperiplanar reactant while E2 is stereospecific.

@a. SN1 and E1 goes with hindered reactant while SN2 and E2 goes with non bulky reactant.

b . Strong nucleophile favor SN2 while strong base favor Elimination.

c. Polar protic solvent favor SN1 and E1 due to stabilization of carbocation formed while polar aprotic solvent favor SN2 and E2 due to solvation of cation nucleophile get free to attack.