Mock  Exam  III  

CH  235-­‐OQ  Summer  2015  

CHEM  101  |  5:30-­‐6:30  pm  

Ques%on  1  

Select  the  weaker  nucleophile  from  each  of  the  following  pairs:  (a)  NH3  or  NH2

-­‐   (b)  Cl-­‐  or  Br-­‐  

Anion  is  a  beDer  Nu-­‐  than  the  neutral  species  

Nucleophilicity  increases  with  halides  as  ion  size  increases  

Ques%on  2  Which  of   the   following  would   react   slowest  under  SN2   reac%on  condi%ons?  

SN2  reac%vity:    1°  >  2°  >  3°  

As  size  of  halide  increases  leaving  group  ability  increases  

Ques%on  3  Explain  why  the  alkyl  halide  shown  below  will  not  undergo  either  SN1  or  SN2  reac%ons.  

3°  alkyl  halide  SN2  highly  unlikely  

What  is  the  hybridiza%on  and  geometry  of  this  carboca%on?  

•  sp3  and  should  be  trigonal  planar  

This  molecule  cannot  adopt  a  trigonal  planar  geometry  due  to  the  bulkiness  of  the  bridgehead  

Ques%on  4  For  each  of  the  following  reac%on,  indicate  whether  the  reac%on  will  proceed  through  an  SN1  or  an  SN2  mechanism  and  give  the  final  product.    Indicate  stereochemistry  where  necessary.  

3°  alkyl  halide  +  polar  pro%c  solvent  +  weak  base  

SN1  

racemic  mixture  

2°  alkyl  halide  +  polar  apro%c  solvent  +  strong  base  

SN2  

inversion  of  stereochemistry  

Ques%on  5  Which  of  the  following  reac%ons  will  be  faster  (I)  or  (II).  What  is  the   type   of   elimina%on   that   will   occur   and   product   of   that  reac%on?  

3°  alkyl  halide  +  polar  pro%c  solvent  +  weak  base  

E1  

2°  alkyl  halide  +  polar  pro%c  solvent  +  weak  base  

E1  

E1  reac%vity:    1°  <  2°  <  3°  

more  stable  carboca%on  -­‐  FASTER  

Ques%on  6  What   are   the   subs%tu%on   and   elimina%on   products   of   the  following  reac%on?    Show  the  full  mechanism  for  each  product.    (Hint:  there  are  four.)  

2°  alkyl  halide  +  polar  pro%c  solvent  +  weak  base  

E1/SN1  

E1  

SN1  

Ques%on  7  Explain  the  difference  in  the  elimina%on  products  produced  from  the  two  reac%ons  with  the  same  star%ng  material.  

3°  alkyl  halide  +  polar  pro%c  solvent  +  weak  base  

E1  

3°  alkyl  halide  +  polar  apro%c  solvent  +  strong  base  

E2  

The  less  subs%tuted  double  bond  will  be  formed  because  the  an%-­‐coplanar  orienta%on  is  needed  

Carboca%on  is  formed  so  proton  removed  to  form  most  stable  double  bond  

Ques%on  8  The   following   reac%on   displays   second   order   kine%cs.     What  would  be  the  major  product  formed?  

Second  order  kine%cs  =  SN2/E2  2°  alkyl  halide  +  strong  base  +  no  heat  

SN2  

Ques%on  9  The   labels  of  4  boDles   in   the   lab   fell  off.  We  don’t  know  which  label  goes  with  which  chemical.  Below  are  the  IR  spectra  of  the  4  compounds.   Match   the   compounds   with   the   correct   chemical  name.  Please  give  a  brief  reason  for  the  match.    a)  3-­‐heptanone  b)  heptanenitrile  c)  ethyl  heptanoate  d)  2-­‐heptanol    

Ques%on  9  

C=O  

sp3  C-­‐H  sp2  C-­‐O  

sp3  C-­‐O  

Ques%on  9  

O-­‐H  sp3  C-­‐H  

Ques%on  9  

CΞN  

sp3  C-­‐H  

Ques%on  9  

C=O  sp3  C-­‐H  

Radicals  

Radical  Chlorina%on  

•  Exothermic  reac%on  •  Proceeds  very  quickly  •  Early  transi%on  state    à  liDle  to  no  regioselec%vity  

57%   43%  

Radicals  

Radical  Bromina%on  

•  Endothermic  reac%on  •  Proceeds  slowly  •  Late  transi%on  state    à  regioselec%vity  

92%   8%  

Radicals  

NBS  •  Brominates  the  allylic  carbon  •  Due  to  radical  intermediates  rearrangment  possible  

Radicals  

Peroxides  •  Effects  hydrohalogena%on  with  bromine  only,  not  chlorine  •  Causes  an%-­‐Markovnikov  addi%on  of  Nu-­‐  

Ques%ons?