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I watched a Khan academy video on organic chemistry functional groups. It mentioned the amine and amide groups.

From what I see, an amide is an amine with a carbonyl group. However, the internet says that that assumption is wrong. I am guessing it has to do with the "R" groups on the amine functional group.

But in the video, he used an example of 2 ethyls (2 carbon chains, not sure what they are called) attached to the nitrogen, and the third R group is just a hydrogen. So what exactly is an R group, and are all amides also amines? Thanks in advance for the help.

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2 Answers 2

up vote 6 down vote accepted

An R group is used in structural formulae as a placeholder for a range of possible subtituents, e.g. hydrogen, alkyl chains or aryl groups etc. It can also be used as an abbreviation when R is a predefined rest.

An amide is a derivative of an organic acid where an $\ce{OH}$ group is substituted by $\ce{NR2}$ (with R = H or any organic rest, see here, for example). An amine is a base, and not formally derived from an acid, but from ammonia. It has the general formula $\ce{NR3}$, with R being H or any organic rest except X=O (X = C, S, etc.) or any other rest derived from an acid. So amides and amines are different classes of compounds. Here are examples for amides of a carboxylic acid, a sulfonic acid (sulfonamide), and an amine (from left to right):

enter image description here

The compound from the video that you have described is diethyl amine. You can formally derive it from ammonia by substituting two hydrogens with ethyl groups:

enter image description here

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Thanks, I didn't know that with R being H or any organic rest except X=O (X = C, S, etc.) . –  simplyianm May 13 at 22:02

While JA is formally correct, the description misses a crucial point, because it is a structural definition.

The reactivity characteristic of amines is their moderate nucleophilicity/basicity and low acidity. This is a property of a lone pair of electrons on the nitrogen.

When a carbonyl is introduced on an alpha-carbon, the electron withdrawing properties, both by induction and resonance, decreases the availability of the lone pair of electrons to engage in reactions as bases. This leads to a strong decrease in nucleophilicity/basicity and a sharp increase in acidity, although amides are still fairly weak acids.

In essence, the difference between amines and amides is that amines are bases, and amides are not.

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