[Skiznibbler]

I've just started learning organic chemistry after learning physical chemistry for about 6 months. I'm trying to familiarize myself with all the common functional groups and classes of molecules. They've all been dead simple up until now. I just started reading about esters.

In the book I'm reading they state

Esters (R1–CO2R2) contain a carboxyl group with an extra alkyl group (CO2R)

but that doesn't make sense to me when I look at a diagram of a carboxyl acid ester on wikipedia

I can see here that the hydroxyl group from the carboxyl has been replaced with an alkoxy group instead. Did they make a mistake in the book saying that esters contain a carboxyl group with an extra alkyl group?

Heres wikipedias definition of esters.

Esters consist of an inorganic or organic acid in which at least one -OH (hydroxy) group is replaced by an -O-alkyl (alkoxy) group.

I'm guessing that definition refers to the class of compounds called esters not the functional group. In the book they must have been talking about carboxyl acid esters. What is the simplest way to think of esters? I'm thinking of them as a functional group which has different types acids as one of its counterparts. Is it only acids with double oxygen bond and hydroxyl group that forms esters?

Heres another example they give on wikipedia


And heres regular phosphoric acid


is the difference between phosphoric acid ester and phosphoric acid the fact that the hydrogen on 1 of the hydroxyl groups has been substituted with an alkyl group?

Its an interesting function group esters. Alot more complex than all the other basic functional groups I've learned. I took a quick glance at amides and they look kinda complicated too.

[macman104]

In the book I'm reading they state

Esters (R1–CO2R2) contain a carboxyl group with an extra alkyl group (CO2R)

but that doesn't make sense to me when I look at a diagram of a carboxyl acid ester on wikipedia
Image cut
I can see here that the hydroxyl group from the carboxyl has been replaced with an alkoxy group instead. Did they make a mistake in the book saying that esters contain a carboxyl group with an extra alkyl group?

Mistake, or just bad wording.  The basic picture from wikipedia above (which I've cut out of my post) is correct.

Heres wikipedias definition of esters.

Esters consist of an inorganic or organic acid in which at least one -OH (hydroxy) group is replaced by an -O-alkyl (alkoxy) group.

I'm guessing that definition refers to the class of compounds called esters not the functional group. In the book they must have been talking about carboxyl acid esters. What is the simplest way to think of esters?

The simplest way is to think of them as a carbonyl group with an alkoxy group attached instead of an OH.

I'm thinking of them as a functional group which has different types acids as one of its counterparts. Is it only acids with double oxygen bond and hydroxyl group that forms esters?

You can form esters from other methods, but one of the most common ways Fischer Esterification uses exactly that method (synthesis from a carboxylic acid).

is the difference between phosphoric acid ester and phosphoric acid the fact that the hydrogen on 1 of the hydroxyl groups has been substituted with an alkyl group?

Indeed.

Its an interesting function group esters. Alot more complex than all the other basic functional groups I've learned. I took a quick glance at amides and they look kinda complicated too.

They're basically the nitrogen counterparts of esters.  Instead of an oxygen connecting the alkyl group, they have a nitrogen.