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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 (1o) amine 
An amine in which nitrogen is bonded to one carbon and two hydrogens.

Secondary (2o) amine: 
An amine in which nitrogen is bonded to two carbons and one hydrogen.

Tertiary (3o) 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



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