Answers:
1) - COOH
2) carboxyl group
The organic acids contain the carboxyl group: - COOH.
Fats are structures composed by fatty acids. Fatty acids are long aliphatic chains with a carboxyl group at the end.
Aminoacids are chains that contains amine group (NH2) at one end and the carboxyl group at the other end.
Then both aminoacids and fatty acids contain the carboxyl group (-COOH) at one end.
Substance a is a base, and substance b is an acid
The following reaction gives a product with the molecular formula C₄H₈O₂. The diagram of the structure of the product can be seen in the image attached below.
The reaction between C₂H₂(ONa)₂ and C₂H₄Br results in the formation of the product C₄H₈O₂ and 2NaBr.
This reaction undergoes an SN₂ mechanism since there is no stable carbocation formed. In the reaction -O⁻Na⁺ attacks the ortho position in C₂H₄Br to form C₄H₈O₂.
In SN₂ mechanism is a nucleophilic substitution reaction where one bond is formed while another one is broken simultaneously.
The mechanism for the reaction can be seen in the image attached below.
Learn more about nucleophilic substitution reaction here:
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