Introduction/Overview/Beginner
Wikipedia: This page provides an overview of carbonyl groups.
Wikipedia: This page provides an overview of nucleophilic substitution.
Chemistry Wikipedia: This page provides an overview of carbonyl substitution.
Intermediate
Nucleophilic Substitution: This page provides an overview of nucleoophilc substitution. It goes into detail on nucleophilic substitutions that involve Hydroxide Ions, Water, Cyanide Ions, and Ammonia.
EXTRA STUFF
Table of Carboxylic Acid Derivatives
TABLE OF REACTIVITY (public site)
Nucleophilic Acyl Substitution: This is video explanation of a general nucleophilic substitution at the carbonyl.
Fischer Esterification: This is a video explanation of an important nucleophilic substitution.