+
H2O
| 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
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
|
B. Ketones
1. IUPAC: Drop the final -e of the stem name and add -one with a locant number.
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
|
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] |
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