ALDEHYDES AND KETONES I. NUCLEOPHILIC ADDITION TO

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					       Chapter 16


ALDEHYDES AND KETONES
          I.
 NUCLEOPHILIC ADDITION
     TO CARBONYL


                    WWU Chemistry
         Reading Assignment
•   DO: Sections 16.0 through 16.7
•   SKIP: Section 16.8
•   DO: 16.9 through 16.18
•   SKIP: Section 16.19
•   DO: Section 16.20
•   Organic Nomenclature: Aldehydes and
    Ketones

                                 WWU Chemistry
          Problem Assignment
• In-Text Problems
  – 16.1 through 16.27
• End-of-Chapter
  –   1 through 6
  –   7a; 7c through 7j
  –   8 b, c, d
  –   9 through 10
  –   12 through 14

                          WWU Chemistry
Aldehyde

         O

         C            R = H, alkyl, aryl
   R         H

Ketone
         O
                  R and R' = alkyl or aryl
         C        R and R' cannot be hydrogen!
    R        R'




                                         WWU Chemistry
IUPAC Nomenclature of Ketones
• Choose the longest continuous carbon chain
  that contains the carbonyl carbon
• Number from the end of the chain closest to
  the carbonyl carbon
• Ending is -one
• Do the ketones section of Organic
  Nomenclature -- Assignment!

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       Example

       O

       C             CH 2
CH 3          CH 2          CH 3


           2-Pentanone




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          Another...
              O

CH 3          C          CH 2
       CH 2       CH            CH 3

                  CH 2
                         CH 3


       4-Ethyl-3-hexanone


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     And another...
         O




               CH   CH3

             CH3

3-Isopropylcyclopentanone
or 3-(1-Methylethyl)cyclopentanone

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   Common, or Trivial, Names
• Name each group attached to the carbonyl
  group as an alkyl group
• Combine into a name, according to:
  – alkyl alkyl’ ketone
• NOTE: This is not all one word!




                                    WWU Chemistry
Example of a Common Name

         O

         C          CH2
   CH3        CH2           CH3

     Methyl propyl ketone



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Another example...

            O

CH3         C           CH3
      CH2         CH2


      Diethyl ketone



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Important example!
          O

          C
    CH3        CH3


   Dimethyl ketone


     Acetone

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Another Important Common Name

                      O

                      C     CH3



       Acetophenone
       (Methyl phenyl ketone)



                                WWU Chemistry
IUPAC Nomenclature of Aldehydes
• Choose the longest continuous carbon chain that
  contains the carbonyl carbon
• Number from the end of the chain closest to the
  carbonyl carbon (this will automatically be carbon
  #1!)
• Ending is -al
• Note: The carbonyl carbon is not identified by
  number in the final name.
• Do the aldehydes section of Organic
  Nomenclature -- Assignment!
                                        WWU Chemistry
              Example
                                   O

           CH2         CH2         C
     CH3         CH2         CH2       H


                 Hexanal

Notice that there is no “-1-” in the name!


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       … another:

       CH 3                        O

       CH            CH 2          C
CH 3          CH 2          CH 2       H



        5-Methylhexanal




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One more:
                   O

       CH2         C
             CH2       H




3-Phenylpropanal



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For cyclic molecules, the ending is
          -carbaldehyde
                    O

                        C   H




        Cycloheptanecarbaldehyde

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Two acceptable alternative
        names:
                           O
                2
                           C
          3                    H

          4            6

                 5

Benzenecarbaldehyde (official IUPAC name)
Benzaldehyde (acceptable IUPAC name)

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Common Names of the Aldehydes
      O                        O                         O

      C                        C                         C
  H         H           CH3        H       CH3 CH2           H
  Formaldehyde            Acetaldehyde      Propionaldehyde
      1                        2                   3
                    O                                        O

                    C                                        C
  CH3 CH2 CH2              H           CH3 CH2 CH2 CH2           H
          Butyraldehyde                        Valeraldehyde
                4                                    5
                                           O

                                           C
             CH3 CH2 CH2 CH2 CH2                 H
                          Caproaldehyde
                                   6


                                                             WWU Chemistry
    Forming Common Names of
            Aldehydes

                                                             O

      C           C        C        C         C        C       C    H





                                                         WWU Chemistry
         Also: “Iso” names:
• Whenever there is a -CH(CH3)2 group, an
  alternative common name is an “iso” name.
• The “iso” name includes all of the carbon
  atoms in the molecule.
• The “iso” name isn’t used if there are other
  substituents.



                                    WWU Chemistry
      Example
      CH3         O

      CH          C
CH3         CH2       H


-Methylbutyraldehyde
Isovaleraldehyde



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     Another example...
                                   O

Br         CH2         CH2         C
     CH2         CH2         CH2       H


      -Bromocaproaldehyde
      -Bromocaproaldehyde




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             Benzaldehyde
                           O
                o-
                           C
         m-                    H

         p-          o-

                m-

ortho (o-)     meta (m-)       para (p-)
1,2-           1,3-            1,4-

                                   WWU Chemistry
More than one subsituent:

                                O

   HO             CH 2          C
           CH 2          CH 2       H


        4-Hydroxybutanal
        -Hydroxybutyraldehyde
        The prefix for -OH is hydroxy

                                    WWU Chemistry
        Also...
                       O

CH3         CH2        C
      CH2         CH       H

                  O
            CH3


2-Methoxypentanal
-Methoxyvaleraldehyde
                               WWU Chemistry
                                          O

                              CH2         C
                                    CH2         H
           CH3

                C
          CH3
                    CH3
                          Bourgeonal



Bourgeonal is thought to be a chemoattractant emitted
by the egg and detected by an odor receptor on the
sperm cell. This guides the sperm to the egg
                                       Science, 299, 2054 (2003)


                                              WWU Chemistry
 Structure of the Carbonyl Group

                       C        O

•Hybridization of the carbonyl carbon is sp2.
•Geometry of the carbonyl carbon is trigonal planar
•Attack by nucleophiles will occur with equal ease
from either the top or the bottom of the carbonyl
group.
•Hybridization of the oxygen is “nominally” sp2.

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                      Prochiral
The carbonyl carbon is prochiral. That is, the carbonyl carbon is
not the center of chirality, but it becomes chiral as the reaction
proceeds.
                               Nu

                                    C   OH
                           R'
         :Nu                    R
                                             These two products
R'
                                             are enantiomers.
     C   O
R
         :Nu                   R
                          R'                 In general, both
                                    C   OH   enantiomers are
                                             formed in equal
                           Nu                amount.

                                                 WWU Chemistry
Reaction of the Carbonyl Group
          with Acids
                                       H
   O                               O
         +     H+
   C                               C




             Typical behavior


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Reaction of the Carbonyl Group
          with Bases
      O                       O

      C                       C


      +                       B


      B:
           Typical behavior


                              WWU Chemistry
   Nucleophilic Addition to
Carbonyl -- General Mechanism
                                         .. _
                                        :O:
    :O :
                            slow
             +       :Nu                 C
     C
                                         Nu

     .. _                                   ..
    :O:                                   : OH
                              fast
    C            +    H2O                    C

    Nu                                       Nu

            NOTE: Reversible reaction

                                        WWU Chemistry
Nucleophilic Addition to Carbonyl --
   in Acid (General Mechanism)
                                         +
     :O :                               :OH
                         fast
                 +
            +   H                       C
      C



                                              ..
      +                                     : OH
    : OH
                           slow
            +   :Nu                           C
     C
                     NOTE: Reversible         Nu
                     reaction

                                         WWU Chemistry
The carbocation intermediate has
          resonance.
             H                              H
        O                              O

        C                              C




The positive charge character on carbon makes
this an excellent site for attack by Lewis bases
(nucleophiles).
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    Once we have the intermediate,
         what happens to it?
    Case 1: The Addition Product is Stable.
                          OH

                    R     C     R

                          Nu
The reaction stops here. This happens most often when
the nucleophilic atom is carbon, oxygen, or sulfur.

                                         WWU Chemistry
Case 2: Addition-Elimination


    OH
                               R        R
R    C   R                         C        +       O
                                                H       H
    Nu                             Nu
         H



The addition product is unstable with respect to loss
of a molecule of water. This is observed most often
when the nucleophilic atom is nitrogen or
phosphorus.

                                            WWU Chemistry
Case 3: Loss of Leaving Group



        O                            O

 R      C    X                  R    C     +   X

        Nu                           Nu



     This process is observed when X is a potential
     leaving group. In this case we have nucleophilic
     acyl substitution (see Chapter 19).


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    What are the stereochemical
          requirements?
• The hybridization of carbon in the carbonyl group
  is sp2
• The geometry around carbon is trigonal-planar.
• Nucleophile can attack the carbonyl group equally
  easily from top or bottom (see model)
• BUT: aldehydes react faster than ketones in
  nucleophilic addition!


                                       WWU Chemistry
                       Why?
• Aldehydes have a hydrogen attached to the
  carbonyl group, whereas ketones have an alkyl
  group.
  – Alkyl groups are much more bulky than hydrogens --
    hence ketones should show some steric hindrance.
• Alkyl groups have a small electron-releasing
  inductive effect.
  – This should make the carbonyl carbon less favorable by
    attack by nucleophile.
• The answer is that there is a combination of steric
  hindrance and inductive effects that makes ketones
  react slower than aldehydes.
                                           WWU Chemistry
    Addition of Cyanide (16.6)
                                      .. _
     :O :                            :O :
                             _
R    C       R   +   CN          R   C       R

                                     CN
      .. _                             ..
     :O :                            : OH
                         +
R    C       R   +   H           R    C      R

     CN                               CN

                                 A cyanohydrin

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                 Mechanism
1)
         O
                                 O
         C            slow
                             R   C       R
     R       R

                                 C
         C   N
                                 N
2)

         O                                   O   H

     R   C   R    +    H+            R       C   R

         C                                   C

         N                                   N


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                       Example
           O                             O
                            Na2CO3
               +   C    N                      C   N
                   (NaCN)



                                     H2O, H+
•Notice that the cyanide ion and
the acid are added in two
                                         OH
separate steps!
•Sodium carbonate is used to                 C     N

keep the reaction medium basic.


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            So, what’s it good for?
                   O                    OH
                           NaCN
              CH2 C    H             CH2 C      C   N
                           H2O
                                         H


Nitriles can be hydrolyzed to form       H2O, H+
carboxylic acids.                        heat

This affords us with an important
method of synthesizing -hydroxy-
                                        OH      O
carboxylic acids -- important
intermediates in biochemical         CH2 C      C   OH
processes.
                                        H


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      Reaction with Organometallic
           Compounds (16.7)

                O                   R                       R
                        ether           .. _ +    H2O
R   MgX +       C               R   C   O : MgX         R   C   OH
                                        ..
            R       R
                                    R                       R




    The products of this sequence are always alcohols.


                                                  WWU Chemistry
      Addition of Organometallic
               Reagents
                                    .. _ +
                    :O :           :O : M

  R   M     +                  R   C      R
                    C
 (R-MgBr)       R          R
                                   R

                                       H2O
                                          +
                                        H
                                     ..
                                   : OH

                               R   C      R     +   M (OH)x
The products of the addition
are always alcohols.               R


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Crude outline of the mechanism
  of organometallic addition
                   R                            R

        -
                                    slow
     "R: "     +        C   O              R    C     O

                   R'                           R'
  (from R-MgX)


                                                     H+
             R, R' = H, alkyl, or aryl

                                                R

                                           R    C     OH

                                                R'


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Whatever is attached to the carbonyl group will be
attached to the resulting alcohol carbon.
                           H                      H

         R    M     +          C    O      R      C     OH

      (M = Li or MgX)      H                    H
                         formaldehyde     primary alcohol

                          R                      R

        R     M    +           C    O      R     C     OH

                          H                    H
                        other aldehydes   secondary alcohol

                          R                      R

        R    M     +           C    O     R      C     OH

                         R'                       R'
                          ketones         tertiary alcohol


                                                      WWU Chemistry
                  Example
       O                              O       MgI
                      CH3MgI
CH3 CH2 C   CH2 CH3            CH3 CH2 C      CH2 CH3
                      ether
                                      CH3


                                           H2O, H+




                                      O       H
Organometallics react with
                               CH3 CH2 C      CH2 CH3
ketones to yield tertiary
alcohols.                              CH3


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                And another...

                 O                MgBr
                                             H2O
      CH3 CH2 CH2 C   H
                          ether               H+

                                                OH

                                  CH3 CH2 CH2 CH


Organometallics react                 1-Phenyl-1-butanol
with aldehydes to form
secondary alcohols


                                                     WWU Chemistry
   Summary of Reactions of
 Organometallics with Carbonyl
        Compounds
• Organometallics with ketones yield tertiary
  alcohols
• Organometallics with aldehydes yield
  secondary alcohols
• Organometallics with formaldehyde yield
  primary alcohols.

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                                 Ethynylation
                                 NaNH 2
H       C       C        H                     H   C     C       Na



            O
                             H    C       C   Na       H+
            C
                                                       H2O
    R               R'

                                                         HO           C    C   H
                                                                 C
One can also use a Grignard                                  R        R'
reagent to do an ethynylation.

                                                                 WWU Chemistry
     To make an alkynyl Grignard...
                   Mg
 CH3 CH2 Br                     CH3 CH2 MgBr
                ether



 R    C   C    H    +       CH3 CH2 MgBr
                                                   ether




                        R   C     C   MgBr     +      CH3 CH2 H


This is an acid-base reaction (the proton is transferred
from the stronger acid to the stronger base).

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      A Practical Application
                   CH 3   O




                              H     C     C      Na



HO
         Estrone                                      OH
                                              CH 3         C   CH




 Used in oral
                   HO
 contraceptives               Ethynylestradiol

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