What is Organic Chemistry?

The field of chemistry which deals with the studies of the properties and structures of compounds that are related to carbon is known as organic chemistry and any chemical compound which shows the presence of C-H bonds is known as organic compounds. Organic chemistry also includes study of organic compounds which has other elements such as oxygen, halogen, silicon, phosphorus, sulfur, and nitrogen.

Introduction to Organic Chemistry

The field of chemistry which deals with the studies of reactions, structures, and properties of organic compounds that comprise carbon bonded through covalent bonding is organic chemistry. The studies regarding the structure of organic compounds could be determined with the help of structural formulas. In order to know about the behavior of organic compounds, a study on the properties has to be done. Both physical properties and chemical properties, the origin of chemical reactivity come under the study regarding the properties of organic compounds. The chemical preparation of polymers, drugs, natural products, and the study of separate organic molecules in the lab come under the study of organic reactions.

In organic chemistry, heterogeneity of chemicals like hydrocarbon (compounds that have both carbon atoms and hydrogen atoms) and compounds that are related to carbon but also shows the presence of other elements such as oxygen, halogen, silicon, phosphorus, sulfur, and nitrogen are studied. Not all compounds that are related to carbon are called organic compounds; certain compounds that show the presence of carbon are inorganic compounds. Examples of compounds that comprise carbon but are considered inorganic compounds are bicarbonate, cyanide, carbon monoxide, etc.

Covalent bonding

Because of the chemical diversity and unique nature of carbon when compared to other elements, carbon is chosen as the primarily focused element in organic chemistry. The reason for the diversity of carbon is listed below:

• The bonds formed by atoms of carbon are stronger with other atoms of carbons.
• The bonds formed by atoms of carbon are stronger with other element’s atoms.
• The number of covalent bonds formed by atoms of carbon is four, which is highest.

Most of the organic compounds show covalent bonding. A chemical bond in which the pairs of electrons are shared among the atoms is named a covalent bond. Bonding pairs or shared pairs is the term used for these pairs of electrons. When atoms shared electrons, there would be a stable balance of repulsive forces and attractive forces among the atoms, and the bonding is covalent bonding. Single bonds, double bonds, and triple bonds are the three categories of covalent bonds. Two bonded electrons are found in a single bond, four bonded electrons are found in double bonds, six bonded electrons are found in triple bonds.

Structural representation of organic compounds

Organic compounds have several kinds of structures. The several ways by which the structure of organic compounds will be depicted are,

• Lewis structure representation.
• Structural formula representation.
• Condensed formula representation.
• Bond-Line formula representation.

Lewis structure representation

One of the primary methods to express the structure of the organic compounds is the Lewis structure. Lewis structures exhibit the bonding among the atoms of a molecule and the electron’s lone pair in a molecule. Each atom and its location in the molecule’s structure with a chemical symbol could be drawn by Lewis structure. The bonds among two atoms are indicated by lines or dots. Lone pairs are indicated as pairs of dots and positioned adjacent to the atoms. An atom of carbon could be joined with a maximum of four dissimilar or same atoms. The Lewis structure of organic compound ethanol is,

But when there is a rise in the size of the compound, it is tough to represent the structure using the help of Lewis structure.

Structural formula representation

The simplified representation of Lewis structures is using a single dash instead of using two electrons covalent bonds. The simplified representation of Lewis's structure is the structural formula. The major focus of the structural formula is on the electrons that are taking part in the bond formation. The structural formula of organic compound ethanol is represented as,

Condensed formula representation

The structural formula could be abbreviated by removing certain or total dashes that indicate the covalent bonds. Identical repeated units are kept in parenthesis and repeated units are represented by the usage of subscripts. In the condensed formulas, parentheses are highly important. For example, the condensed structural formula of CH₃CH₂CH₂CH₂CH₂CH₂CH₃ is CH₃(CH₂)₅CH₃.

Bond line representation

The hydrogen atoms and atoms of carbon are not expressed in bond line representation for the organic compounds’ structure. The lines indicating the bonds of carbon-carbon are drawn in a zig-zag manner. Bond line representation represents the heteroatoms. The ends present in bond-line structures express methyl group when no functional group is found whereas the junctions of a line indicate the atoms of carbon linked to specific hydrogen atoms needed to satisfy the carbon atom’s valency. The bond line representation of organic compound ethanol is represented as,

Several types of organic compounds

Organic compounds that comprise hydrogen atoms and carbon atoms are called hydrocarbons. Hydrocarbons could be categorized into,

• Aliphatic compounds.
• Aromatic compounds.

Aliphatic compounds

An organic compound in which hydrogen atoms and carbon atoms are linked together in a straight chain is termed an aliphatic compound. Alkynes, alkanes, and alkenes are the major categories of aliphatic compounds.

Alkane is a hydrocarbon, which comprises carbon-carbon, carbon-hydrogen in single bonds. They are saturated compounds. Ethane comes under the category alkane.

Alkene is a hydrocarbon, which comprises one double bond or more than one double bond. Ethene is an alkene.

Alkyne is a hydrocarbon, which comprises one triple bond or more than one triple bond. Ethyne is an alkyne.

Both alkenes and alkynes come under unsaturated compounds. Unsaturated compounds, as well as saturated compounds, are seen as cyclic derivatives. Single bonds are found in saturated cyclic compounds but the alternating double bond is seen in aromatic rings. Multiple bonds are seen in both cycloalkenes and cycloalkynes but cycloalkanes do not.

Aromatic compounds

Organic compounds which show the presence of alternate double bonds are aromatic compounds. The hybridization of every atom present in the ring could be sp² hybridized, and this permits the addition of stability. Cyclic compounds that are aromatic in nature could follow Huckel’s rule and cyclic compounds that are anti-aromatic would follow the 4n rule.

Functional group

The chemical properties along with the physical properties of an organic compound are obtained by an atom or by a collection of atoms named as a functional group. The organic compounds are named according to the functional group.

An organic compound where a hydroxyl group (OH group) is replaced for a hydrogen atom, then the functional group present is alcohol.

In an organic compound, when an atom of carbon is seen in a double bond with oxygen and is singly bonded with a hydroxyl group, then the functional group present is carboxylic acids. Ethanoic acid comes under carboxylic acid.

Ketones, aldehydes, amines, amides, ether, and thiols are several other functional groups.

Isomers

Molecules, which contain an equal number of atoms of each element whereas the arrangement would be different, then the molecules are considered as an isomer. The molecular formula of the organic molecules would be the same whereas the chemical structure would be different. Structural isomerism and stereoisomerism are two major categories of isomerism.

When the organic molecules would have an equal number of bonds and atoms whereas the arrangement of atoms could be different, then they are said to be structural isomers.

When the organic molecules contain the same structural formula and molecular formula whereas the arrangement of bonds in space could be different, then they are said to be stereoisomers.

Context and Applications

This topic is needed for bachelor's in chemistry and bachelor's in biochemistry.

Practice Problems

Question 1: The given compound below is an example of which functional group?

1. Carboxylic acids
2. Aldehyde
3. Ketone
4. Alcohol

Answer: Option (3) is correct.

Explanation: The given compound is an example of ketone as the carbonyl group is present (carbon double-bonded with oxygen) attached to two same alkyl groups.

Question 2: The name of the group that is formed when one atom of hydrogen is eliminated from an alkane compound.

1. Alkene
2. Aldehyde
3. Ketone
4. Alkyl

Answer: Option (4) is correct.

Explanation: When one atom of hydrogen is removed from an alkane, then the alkyl group is obtained.

Question 3: Among the following, the IUPAC name of compounds, which contain triple bonds ends with?

1. -ane
2. -ene
3. -yne
4. -ol

Answer: Option (3) is correct.

Explanation: Compounds, which have triple bonds are alkynes. The IUPAC name of compounds that contain triple bond ends with yne.

Question 4: Give pentane’s molecular formula.

1. C₅H₁₁
2. C₆H₁₂
3. C₅H₁₂
4. C₆H₁₁

Answer: Option (3) is correct.

Explanation: Pentane has five carbon atoms and twelve hydrogen atoms. Pentane’s molecular formula is C₅H₁₂.

Question 5: Among the following, which is an example of alcohol?

1. Methanol
2. Methane
3. Methanal
4. Methyl

Answer: Option (1) is correct.

Explanation: Alcohols have -OH functional group. Methanol is alcohol whose formula is CH₃OH.