Solvolysis occurs when a) the solvent acts as the substrate b) the solvent acts

Question

Solvolysis occurs when a) the solvent acts as the substrate b) the solvent acts as the nucleophile. c) the solvent dissociates the substrate. d) the solvent traps the counter-ion. 2. What happens to the rate of an S_N1 reaction if the nucleophile concentration is doubled? a) The reaction rate doubles. b) The reaction rate is halved. c) The reaction rate increases by four times d) The reaction rate is unaffected. 3 Which statement is TRUE about an S_N2 reaction? a) It involves a carbocation intermediate. c) It can work with a polar aprotlc solvent. c) It has two transition states. d) None of the above. 4. Which substitution reaction below is the most favorable? a) Methyl bromide + HS rightarrow b) Methyl fluoride + HS rightarrow C) Methyl bromide + NH_3 rightarrow d) Methyl fluoride + NH_3 rightarrow 5. The formula for a substitution reaction is a) a weak base always substitutes for a strong base. b) a strong base always substitutes for a weak base. c) a weak base always serves as a poor leaving group. d) a strong base always serves as a good leaving group. 6. With two chiral centers present, which pair of these stereoisomers is a pair of enantiomers? a) (S,R) & (S,S) b) (R,R) & (R,S) c) (R,S) & (S,R) d) (S,S) & (R,S) 7. Which statement is true about an S_N1 reaction? a) It has Walden inversion. b) It needs to have a strong base as a nucleophile. c) It is a two-step reaction. d) A methyl halide is the best for S_N1 reaction. 8. Which one can be the best nucleophile as below? a) NaOCH_3 b) H_20 c) CH_3OH d) NH(CH_3)_2 9. What is the purpose of adding crown ether like 18-crown-6 ether to a substitution reaction? a) It makes the substrate to lose its leaving group easier. b) It makes the electrophilic carbon of the substrate to be more electrophilic. c) It causes the nucleophile to have an extra pair of electrons.

Explanation / Answer

1.   (b)

2. (d) Because the rate limiting step is the formation of carbocation.

3.    (c) It work faster in polar aprotic solvents

4.    (a) Because Br- is good leavimg group and HS- is a better nucleophile.

5.    (a)

6.    (c) (RS) and (SR) at similar position opposite configuration.

7.    (c) a two step reaction: first formation of carbocation and second attack of nucleophile to carbocation.

8.   (a) NaOCH3   because charged nucleophiles are best (Na+ -OCH3)

9. (c) IT takes the metal ion from nucleophile and makes free negative chargeon nucleophile.

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