Acetic Acid CH3COOH not C2H4O2
I am researching CH3COOH (acetic acid), and my question
is why do acid's have the extra OH at the end? Why is that extra OH not
add in to the formula? Basically I wish to know why it is not C2H4O2
instead of CH3COOH?
Both notations are correct but the notation that has the group 'COOH' is
used to make it obvious that you are dealing with an acid. All organic
acids have this grouping - an Oxygen atom double-bonded to Carbon and a
Hydroxy group bonded to the same carbon. The Hydrogen atom in this group is
readily available for acid chemistry.
Writing the chemical formula (called a compressed chemical
structure) makes the formula easier to read and allows the writer to
be very specific about which compound the writer is talking about.
Think of the empirical formula for acetic acid: C2H4O2 - using that
formula we can write many different -and correct- chemical
structures: (1) O=CH-CH2-OH, (2) HO-CH=CH-OH, (3) CH3-O-CH=O, (4)
CH3-COOH - all of which are acceptable Lewis Structures. So, if we
want to be specific, we need to state that we are talking about
acetic acid or the compound we the arrangement: CH3COOH.
Greg (Roberto Gregorius)
The formula C2H4O2 only gives the molar amounts of the elements C, H, and
O. The notation CH3COOH attempts to describe how the atoms are connected
in more detail, specifically: CH3--C//O--OH which does not translate very
well in the fonts available. Talking through the structure, a CH3--
(methyl group) is connected to a carbon atom: CH3--C. The second carbon
atom, on the right is doubly bonded to an oxygen atom and to a hydroxyl
The "H" connected to the "O" ionizes in water to form the ionized form of
acetic acid. This provides more information regarding the molecular
structure of acetic acid. It is difficult to draw the structure given the
font limitations. The "H" 's bonded to the carbon atom in the fragment
"CH3--" are covalently bonded and do not ionize.
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Update: June 2012