Introduction to Organic Chemistry and Functional Groups

Introduction to Organic Chemistry

What is Organic Chemistry?

Organic chemistry is the branch of chemistry that studies compounds primarily composed of carbon and hydrogen, often with oxygen, nitrogen, sulfur, and halogens. Organic compounds are the basis of all life and are found in fuels, medicines, plastics, and foods.

• Organic compounds contain carbon atoms bonded to hydrogen and possibly other elements (O, N, S, halogens).

• They are typically covalent, have low melting and boiling points, are flammable, and are soluble in nonpolar solvents but not in water.

• Examples: gasoline, medicines, shampoos, plastics, perfumes, foods.

Organic vs. Inorganic Compounds

Organic and inorganic compounds differ in their composition, bonding, and properties.

• Organic: C and H (sometimes O, S, N, P, or halogens), mostly covalent bonds, nonpolar, low melting/boiling points, flammable, not water soluble.

• Inorganic: Metals and nonmetals, often ionic bonds, polar, high melting/boiling points, not flammable, water soluble.

Property	Organic	Example: C3H8	Inorganic	Example: NaCl
Elements Present	C and H, sometimes O, S, N, P, or Cl (F, Br, I)	C and H	Most metals and nonmetals	Na and Cl
Particles	Molecules	C3H8	Mostly ions	Na+ and Cl-
Bonding	Mostly covalent	—	Many are ionic, some covalent	—
Polarity of Bonds	Nonpolar, unless a strongly electronegative atom is present	—	Most are ionic or polar covalent, a few are nonpolar covalent	Ionic
Melting Point	Usually low	-188°C	Usually high	801°C
Boiling Point	Usually low	-42°C	Usually high	1413°C
Flammability	High	Burns in air	Low	Does not burn
Solubility in Water	Not soluble unless a polar group is present	—	Most are soluble unless nonpolar	Yes

Structure and Bonding in Organic Compounds

Covalent Bonds and the Octet Rule

Carbon forms four covalent bonds to achieve a stable octet, while hydrogen forms one bond. Other elements commonly found in organic compounds have characteristic bonding patterns.

• Carbon: 4 bonds

• Hydrogen: 1 bond

• Nitrogen: 3 bonds

• Oxygen/Sulfur: 2 bonds

• Halogens: 1 bond

Element	Group	Covalent Bonds	Structure of Atoms
H	1A (1)	1	H—
C	4A (14)	4	—C—
N	5A (15)	3	—N—
O, S	6A (16)	2	—O—
F, Cl, Br, I	7A (17)	1	—X

Tetrahedral Structure of Carbon

According to VSEPR theory, a carbon atom with four single bonds adopts a tetrahedral geometry with bond angles of 109.5°.

Alkanes: Structure and Nomenclature

Alkanes are saturated hydrocarbons with only single bonds. Their general formula is $C_nH_{2n+2}$.

• Names end in -ane (e.g., methane, ethane, propane).

• Can be represented by expanded, condensed, or line-angle formulas.

Number of Carbon Atoms	IUPAC Name	Molecular Formula	Condensed Structural Formula	Line-Angle Formula
1	Methane	CH4	CH4	—
2	Ethane	C2H6	CH3—CH3	—
3	Propane	C3H8	CH3—CH2—CH3	—
4	Butane	C4H10	CH3—CH2—CH2—CH3	—
5	Pentane	C5H12	CH3—CH2—CH2—CH2—CH3	—
6	Hexane	C6H14	CH3—CH2—CH2—CH2—CH2—CH3	—
7	Heptane	C7H16	CH3—(CH2)5—CH3	—
8	Octane	C8H18	CH3—(CH2)6—CH3	—
9	Nonane	C9H20	CH3—(CH2)7—CH3	—
10	Decane	C10H22	CH3—(CH2)8—CH3	—

Cycloalkanes

Cycloalkanes are saturated hydrocarbons with carbon atoms arranged in a ring. They have two fewer hydrogens than the corresponding open-chain alkane.

Name	Ball-and-Stick Model	Condensed Structural Formula	Line-Angle Formula
Cyclopropane	Model	CH2CH2CH2	Triangle
Cyclobutane	Model	CH2CH2CH2CH2	Square
Cyclopentane	Model	CH2CH2CH2CH2CH2	Pentagon
Cyclohexane	Model	CH2CH2CH2CH2CH2CH2	Hexagon

Substituents and Alkyl Groups

Alkyl and Halo Substituents

Substituents are groups attached to the main carbon chain. Alkyl groups are derived from alkanes by removing one hydrogen and are named with a -yl ending. Halogen substituents are named as halo- (fluoro, chloro, bromo, iodo).

Formula	Name	Formula	Name
CH3—	methyl	CH3CH2—	ethyl
CH3CH2CH2—	propyl	CH3CH2CH2CH2—	butyl
F—	fluoro	Cl—	chloro
Br—	bromo	I—	iodo

Physical Properties and Uses of Alkanes

Physical Properties

• Alkanes are nonpolar, insoluble in water, less dense than water, and flammable.

• Alkanes with 1–4 carbons are gases (e.g., methane, propane, butane).

• Alkanes with 5–8 carbons are volatile liquids (e.g., gasoline components).

• Alkanes with 9–17 carbons are higher boiling liquids (kerosene, diesel, jet fuel).

• Alkanes with 18 or more carbons are waxy solids (used in coatings).

Combustion of Alkanes

Alkanes undergo combustion reactions with oxygen to produce carbon dioxide, water, and energy.

• General equation: $\text{Alkane} + O_2 \rightarrow CO_2 + H_2O + \text{energy}$

Functional Groups in Organic Chemistry

Definition and Importance

Functional groups are specific groups of atoms within molecules that determine the characteristic chemical reactions of those molecules. They are used to classify organic compounds into families.

• Examples: alkanes, alkenes, alkynes, aromatics, alcohols, ethers, thiols, aldehydes, ketones, carboxylic acids, esters, amines, amides.

Hydrocarbons: Saturated and Unsaturated

Saturated Hydrocarbons

Saturated hydrocarbons (alkanes and cycloalkanes) have only single bonds and the maximum number of hydrogen atoms per carbon.

• Examples: hexane, cyclohexane, branched alkanes.

Unsaturated Hydrocarbons

Unsaturated hydrocarbons have double or triple bonds, resulting in fewer hydrogens per carbon.

• Alkenes: contain at least one C=C double bond (bond angle 120°).

• Alkynes: contain at least one C≡C triple bond (bond angle 180°).

Alkenes, Alkynes, and Aromatic Compounds

Alkenes

Alkenes are named by replacing the -ane ending of the corresponding alkane with -ene. The simplest alkene is ethene (ethylene).

• Example: $H_2C=CH_2$ (ethene/ethylene)

Alkynes

Alkynes are named by replacing the -ane ending with -yne. The simplest alkyne is ethyne (acetylene).

• Example: $HC\equiv CH$ (ethyne/acetylene)

Aromatic Compounds

Aromatic compounds contain a benzene ring, a planar ring of six carbon atoms with alternating double and single bonds (delocalized electrons).

Cis-Trans Isomerism in Alkenes

Cis-Trans Isomers

Alkenes can exhibit cis-trans isomerism due to restricted rotation around the double bond. In cis isomers, similar groups are on the same side; in trans isomers, they are on opposite sides.

Alcohols, Ethers, and Thiols

Alcohols

Alcohols contain a hydroxyl group (–OH) attached to a carbon atom. They are named by replacing the -e of the alkane with -ol (e.g., methanol, ethanol).

• Alcohols with 1–4 carbons are soluble in water; those with more are less soluble.

• Alcohols have higher boiling points than alkanes due to hydrogen bonding.

Ethers

Ethers have an oxygen atom bonded to two carbon groups (R–O–R'). They are named by listing the alkyl groups followed by 'ether' (e.g., dimethyl ether).

Thiols

Thiols contain a sulfhydryl group (–SH) and often have strong odors. They are found in foods like onions and garlic and are used as odorants for gas leaks.

Aldehydes and Ketones

Structure and Properties

Aldehydes and ketones both contain a carbonyl group (C=O). In aldehydes, the carbonyl is at the end of the chain (R–CHO); in ketones, it is within the chain (RCOR').

Carboxylic Acids, Esters, and Amides

Carboxylic Acids

Carboxylic acids contain a carboxyl group (–COOH). They are weak acids and ionize in water to form carboxylate ions.

Esters

Esters are derived from carboxylic acids and alcohols. They are responsible for the aromas and flavors of many fruits and flowers.

Amides

Amides are formed when the –OH group of a carboxylic acid is replaced by an –NH2 group. They are important in biology and medicine (e.g., urea, barbiturates).

Amines and Alkaloids

Amines

Amines are derivatives of ammonia (NH3) with one or more alkyl or aromatic groups attached to nitrogen. They have characteristic odors and can form amine salts when neutralized by acids.

Alkaloids

Alkaloids are naturally occurring amines found in plants. Many are physiologically active and used as drugs (e.g., morphine, codeine, caffeine, nicotine).

Chirality in Organic Molecules

Chiral and Achiral Objects

Chiral molecules are non-superimposable on their mirror images, much like left and right hands. Chirality is important in biological systems because enantiomers can have different biological activities.

• A chiral carbon is bonded to four different groups.

• Enantiomers are pairs of chiral molecules that are mirror images of each other.