Functional Groups in Organic Chemistry

Functional Groups

** Carbon combines with other atoms (e.g., H, N, O, S, halogens) to form structural units called functional groups.

** Functional groups are important for three reasons. First, they are the units by which we divide organic compounds into classes. Second, they are sites of characteristic chemical reactions. A particular functional group, in all compounds that contain it, undergoes the same types of chemical reactions.

** In addition to the reason up , functional groups serve as a basis for naming organic compounds. therefore there are a lot of Functional groups.

** Hence, We introduce here several of the functional groups. We shall have more to say about the structure and properties of these functional groups in following chapters

(1) Alcohols

** The functional group of an alcohol is an -OH (hydroxyl) group bonded to a tetrahedral carbon atom (a carbon having single bonds to four other atoms).

** Here is the Lewis structure of ethanol.

** We can also represent this alcohol in a more abbreviated form called a condensed structural formula.

** In a condensed structural formula, CH₃ indicates a carbon bonded to three hydrogens, CH₂ indicates a carbon bonded to two hydrogens, and CH indicates a carbon bonded to one hydrogen.

** In a condensed structural formula, we can write alcohol formula without Unshared pairs of electrons(Oxygen) .

** Thus, the condensed structural formula for the alcohol with molecular formula C₂H₆O is CH₃-CH₂-OH. It is also common to write these formulas in an even more condensed manner, by omitting all single bonds: CH₃CH₂OH.

** Alcohols are classified as primary (1°), secondary (2°), or tertiary (3°) depending on the number of carbon atoms bonded to the carbon bearing the -OH group.

Primary alcohols  (1°) 

A compound containing a functional group bonded to a carbon atom bonded to only one other carbon atom and two hydrogens.

Secondary alcohols  (2°)

A compound containing a functional group bonded to a carbon atom bonded to two other carbon atoms and one hydrogen atom.

Tertiary alcohols (3°) 

A compound containing a functional group bonded to a carbon atom bonded to three other carbon atoms.

(2) Amines

** The functional group of an amine is an amino group, a nitrogen atom bonded to one, two, or three carbon atom(s) by single bonds.

** In a primary (1°) amine, nitrogen is bonded to one carbon atom. In a secondary (2°) amine, it is bonded to two carbon atoms, and in a tertiary (3°) amine, it is bonded to three carbon atoms.

** Notice that this classification scheme is different from that used with alcohols and halides.

Amino group 

A compound containing a nitrogen atom bonded to one, two, or three carbon atom(s) by single bonds.

Primary (1^o) amine 

An amine in which nitrogen is bonded to one carbon and two hydrogens.

Secondary (2^o) amine: 

An amine in which nitrogen is bonded to two carbons and one hydrogen.

Tertiary (3^o) amine: 

An amine in which nitrogen is bonded to three carbons.

(3) Aldehydes and Ketones

** The functional group of both aldehydes and ketones is the C=O (carbonyl) group.

** formaldehyde, CH₂O, is the simplest aldehyde, the carbonyl carbon is bonded to two hydrogens. In all other aldehydes, it is bonded to one hydrogen and one carbon.

** In a condensed structural formula, the aldehyde group may be written showing the carbon oxygen double bond as -CH=O; alternatively, it may be written -CHO.

** In a ketone, the carbonyl carbon is bonded to two carbon atoms.

Carbonyl group

A C = O group.

Aldehyde 

A compound containing a -CHO group.

Ketone 

A compound containing a carbonyl group bonded to two carbons.

(4) Carboxylic Acids

** The functional group of a carboxylic acid is a -COOH (carboxyl: carbonyl+ hydroxyl) group.

** In a condensed structural formula, we can write a carboxyl group like this  -CO₂H.

Carboxylic acid:

A compound containing a carboxyl, -COOH, group.

Carboxyl group:

A -COOH group.

(5) Esters

A carboxylic ester, commonly referred to as an ester, is a derivative of a carboxylic acid in which the hydrogen of the carboxyl group is replaced by a carbon- containing group.

Carboxylic ester: 

A derivative of a carboxylic acid in which H of the carboxyl group is replaced by a carbon.

(6) Amides

** The last functional group we will explain here is A carboxylic amide, it is commonly referred to as an amide, is a derivative of a carboxylic acid in which the -OH of the carboxyl group is replaced by an amine.

** As the model shows, the group is planar, something we will explain later.

Amide: 

A derivative of a carboxylic acid in which the -OH is replaced by an amine.

(7) Common Functional groups used in Organic Chemistry

In conclusion, the table blow indicates most of all Functional groups used in Organic Chemistry:

Reference: Organic chemistry / William H. Brown , Christopher S. Foote , Brent L. Iverson , Eric V. Anslyn , Bruce M. Novak . ( sixth edition) . United States