[Skiznibbler]

I'm having a bit of trouble understanding esters. So from what I've gathered an ester always has an acid counterpart. For every ester there is an acid. An ester is the acid with the hydroxyl group replaced with a methoxy group. Thats fairly simple but I'm wondering what kinds of acids we're talking about here. Does the acid have to have a carbonyl group or at least an oxygen atom doubly bonded to another atom? In the case of carboxyl acid the oxygen has a double bond to the carbon but in the case of phosphoric acid the oxygen has a double bond to phosphorus so obviously the acid doesn't have to have a carbonyl group to form an ester.

So basically the acid has to have its main atom whether it be carbon, sulfur, phosphorus, or nitrogen etc. doubly bonded to an oxygen atom and have at least one hydroxyl group and if one of the hydroxyl groups is replaced with a methoxy group then that molecule will become an ester. Is that correct? Do these acids fall under a class or category? Do all acids have this hydroxyl group and double oxygen bond or is it only certain acids that fit this criteria?

Also I noticed when I was looking at a particular ester on wiki this is what they said

Ethyl cinnamate is the ester of cinnamic acid and ethanol.

I can see how it is an ester of cinnamic acid but I don't understand why they mention ethanol. Whats ethanol got to do with this ester?

[Transmutation]

An ester is the condensation product of an alcohol and an acid.  This means that one molecule of acid and one molecule of alcohol combine to form one molecule of ester + one molecule of water.  Typically the acid is a carboxylic acid, but there are also some esters based on inorganic acid moieties such as phosphate and sulfonate esters.  The alcohol can also be replaced by a thiol to form a thioester.1

The best known esterification reaction is called Fischer esterification.  Acid catalyzes this reaction.  If you would like to draw the mechanism, I will quickly describe it for you.

1) Protonate the carbonyl group of the carboxylic acid.
2) Nucleophilic attack on the carbonyl by the alcohol to form a tetrahedral intermediate.
3) Proton transfer from the alcohol to one of the two hydroxyl groups in the tetrahedral intermediate.
4) Reformation of the carbonyl with expulsion of water as a leaving group.
5) Deprotonation of the carbonyl (upon workup).

Note that Fischer esterification is a reversible reaction; it is driven to form products by use of a large excess of the alcohol.  This usually means using the alcohol in question as the reaction solvent.  The alcohol does not have to be methanol.  One could use ethanol, isopropanol, butanol, etc.

Hope this clears things up for you.

[Arkcon]

I'm having a bit of trouble understanding esters. So from what I've gathered an ester always has an acid counterpart. For every ester there is an acid. An ester is the acid with the hydroxyl group replaced with a methoxy group.

Let's start here.  The hydroxyl group of the carboxyl group can be replaced with any of a number of alcohols, so you don't have to restrict yourself to a methoxy only.  Hence your example of ethyl cinnamate.  Another very important ester is ethyl acetate, made from ethanol and acetic acid.

Did you get a chance to see all these?  It almost makes me hungry:
http://en.wikipedia.org/wiki/Ester#Physical_properties

[Skiznibbler]

Ah yeah I get it now thanks alot. One thing I don't get though is what do they mean when they say it condenses? In chemistry the only meaning I know for condensation is when a vapor condenses into a liquid.

[Arkcon]

Yeah, chemical jargon strikes again.  See why it's hard to explain things to people who haven't taken any chemistry?  Look at this definition here:

http://en.wikipedia.org/wiki/Condensation_reaction

This is quite a common term in organic chemistry.