CHEM 30 B   Dr. R. Rinehart

Chapter 14 ALDEHYDES and KETONES

 

Carbonyl Containing Functional Groups
-- Slides by Warren Gallagher at the University of Wisconsin, Eau Claire
http://www.chem.uwec.edu/Chem150_S06/Pages/lecture-materials.html > Lecture 5
Aldehydes and ketones by Gary Trammell and Srinivas Vuppuluri
at the University of Illinois at Springfield
http://people.uis.edu/gtram1/organic/carbonylmenu.htm
 

            This chapter is deceptively short, but quite important. Aldehydes and both contain the carbonyl  [C=O] group; in aldehydes, RCHO, a hydrogen is attached to one side of the carbonyl carbon, while in ketones, the carbonyl group is “sandwiched” between two other carbon atoms. In the last chapter, we saw that aldehydes originate from the oxidation of primary alcohols and ketones from the oxidation of secondary alcohols.  

I.   NOMENCLATURE: first, locate the longest chain containing the carbonyl group.
           
A.   ALDEHYDES:  [T
                       
1. IUPAC: the -
CHO group is always at the end of a chain; its carbon is
 
                                    automatically given #1. Drop the final -e of the stem name and add -al.
                                               
e.g., CH3CHO is ethanal.
                       
2. Common: the name is related to that of the corresponding carboxylic acid.

                                    e.g., CH3CHO is “acetaldehyde”, since CH3CO2H is acetic acid.

see my table of  aldehydes

See Dave Woodcock’s Chime structures of aldehydes at OUC at
http://www.molecularmodels.ca/molecule/Aldehydes.htm 

  
         
B.  
Ketones 
                       
1. IUPAC:
Drop the final -e of the stem name and add -one with a locant number.                                     e.g., CH3CH2COCH2CH3 is 3-pentanone.
                       
2. Common: name the two groups on either side of the carbonyl group. Thus,

                                    acetone, CH3COCH3 can also be called “dimethyl ketone” and

                                    CH3COCH2CH3 is methyl ethyl ketone.

see my table of  ketones

See Dave Woodcock’s Chime structures of ketones at
http://www.molecularmodels.ca/molecule/Ketones.htm 

            C.   In MULTIFUNCTIONAL COMPOUNDS, the order of priority for numbering chains

                        is:    -CHO  >  -OH  >  -C=O  >  C=C  >  C≡C  >  X or R

Basic Organic Nomenclature by Dave Woodcock at OUC [requires Chime]
http://www.molecularmodels.ca/nomenclature/index-2.htm 

         D.   CARBOHYDRATES [Chapter 17] are polyhydroxy aldehydes or ketones  

II.   Physical Properties: [
           
A.  Boiling points: Higher than alkanes of similar molecular weight [C=O is polar]

                        but lower than corresponding alcohols [no polarized H for H-bonding]

            B.   Solubility in water: Since water can H-bond to the carbonyl oxygen, aldehydes

                        and ketones with <6 carbons are water-soluble. Most aldehydes and ketones

                        will dissolve in alcohols and ethers.

            C. Odor: low-m.w. aldehydes often have unpleasant odors, but some higher-m.w. aldehydes smell

                        rather pleasant; low-m.w. ketones have somewhat sharp odors, but larger ketones
                         frequently have very pleasant smells. See the tables for examples.
 

III.   CHEMICAL PROPERTIES and REACTIONS: yes, they are flammable [burn, baby, burn!]       

A.      OXIDATION [with Cr(VI), Mn(VI), Cu(II), or Ag(I)]:

                        1.  ALDEHYDES: yield corresponding carboxylic acid

                        2.   KETONES: no reaction

                        3.   Tollens’ test: aldehydes reduce Ag+ to Ag0; MIRROR formation

                        4.   Benedict’s or Fehling’s test: carbohydrates can reduce Cu+2 to Cu+1

                                                a brick-red precipitate of Cu2O forms

            B   .REDUCTION: [addition of hydrogen [H2] in presence of Pt catalyst]

                        1 . Aldehydes yield primary alcohols.

2.      Ketones yield secondary alcohols  

C.        ADDITION of ALCOHOLS [especially important for carbohydrates]

 

   + H2O

aldehyde            +        alcohol             -à                                hemiacetal           { + second molecule of R’’OH}   -à       acetal      (+water)

(or ketone)                                                                        (or hemiketal)                                                                            (or ketal)

                                                                                               

                                                                                                                                                         

            D.   Reaction with amino groups [not in book at this point but it’s important – see the lab]  

                           RR’ C=O      +       H2N-R”         ---------->           RR’C=N-R”           +         H2O  

                         aldehyde or ketone        +             amine           --à                imine or “Schiff base”            +            water

                         

   

there's more information on those oxidation reactions and reactions with amines in this week's lab!

© Ronald W. Rinehart, 2002, 2004   Close this window to return to class schedule or click here