Chapter 11: Introduction to Organic Chemistry – Hydrocarbons, Alkanes, Alkenes, Alkynes, and Nomenclature

Chapter 11: Introduction to Organic Chemistry

11.1 Organic Compounds

Organic compounds are chemical substances containing carbon atoms, typically bonded to hydrogen, oxygen, nitrogen, and other elements. The vast majority of organic compounds are based on carbon's ability to form stable covalent bonds with itself and other atoms, leading to a wide variety of molecular structures.

• Hydrocarbons are the simplest organic compounds, consisting only of carbon and hydrogen.

• Organic chemistry studies the structure, properties, and reactions of these compounds.

11.2 Alkanes

Alkanes are saturated hydrocarbons containing only single bonds between carbon atoms. Their general formula is $C_nH_{2n+2}$.

• Each carbon atom forms four single covalent bonds.

• Examples: Methane ($CH_4$), Ethane ($C_2H_6$), Propane ($C_3H_8$).

11.3 Alkanes with Substituents

Alkanes can have branches or substituents, such as alkyl groups or halogens, attached to the main carbon chain. The International Union of Pure and Applied Chemistry (IUPAC) system provides rules for naming these compounds.

• Step 1: Identify the longest continuous carbon chain as the parent hydrocarbon.

• Step 2: Number the carbon atoms in the chain starting from the end nearest a substituent.

• Step 3: Name and locate each substituent (in alphabetical order) as a prefix to the parent name.

Example:

Structure	Substituents	Parent Chain	IUPAC Name
CH3-CH(CH3)-CH2-CH(CH3)-CH3	2,3-dimethyl	Pentane (5C)	2,3-dimethylpentane
CH3-CH2-CH(CH3)-CH2-CH(CH2CH3)-CH2-CH3	3-methyl, 5-ethyl	Octane (8C)	5-ethyl-3-methyloctane

Multiple Substituents: Use prefixes di-, tri-, tetra- for identical substituents and separate their positions with commas (e.g., 2,2-dibromobutane).

Haloalkanes

Haloalkanes are alkanes in which one or more hydrogen atoms are replaced by halogen atoms (F, Cl, Br, I). Halogens are treated as substituents and named as prefixes (fluoro-, chloro-, bromo-, iodo-).

• Halogen substituents are listed first in the name, in alphabetical order.

• Number the chain to give the lowest possible numbers to the substituents.

Example:

Structure	Substituents	Parent Chain	IUPAC Name
CH3-CH(Cl)-CH(Cl)-CH2-CH3	2,3-dichloro	Pentane	2,3-dichloropentane
CH3-CH2-C(Br)2-CH3	2,2-dibromo	Butane	2,2-dibromobutane

11.5 Alkenes and Alkynes

Alkenes and alkynes are unsaturated hydrocarbons containing double and triple bonds, respectively. Their general formulas are:

• Alkene: $C_nH_{2n}$

• Alkyne: $C_nH_{2n-2}$

Each carbon atom forms four bonds, and the presence of multiple bonds affects the compound's reactivity and physical properties.

Type	General Formula	Example	Condensed Formula
Alkane	$C_nH_{2n+2}$	Ethane	CH3CH3
Alkene	$C_nH_{2n}$	Ethene	CH2=CH2
Alkyne	$C_nH_{2n-2}$	Ethyne	HC≡CH

Physical Properties of Alkenes and Alkynes

Alkenes and alkynes share similar physical properties with alkanes:

• Non-polar compounds

• Not soluble in water

• Highly soluble in non-polar solvents

• Boiling and melting points increase with molecular weight

11.6 Nomenclature of Alkenes and Alkynes

Naming alkenes and alkynes follows similar rules to alkanes, with additional steps for locating multiple bonds:

• Step 1: Identify the longest carbon chain containing the double or triple bond.

• Step 2: Number the chain from the end nearest the multiple bond.

• Step 3: Indicate the position of the double/triple bond and any substituents (alphabetical order).

Examples:

Structure	Substituents	Parent Chain	IUPAC Name
CH3-CH(CH3)-CH=CH-CH3	4-methyl	Pentene (5C)	4-methyl-2-pentene
HC≡C-CH(CH3)-CH3	3-methyl	Butyne (4C)	3-methyl-1-butyne
CH3-CH(CH3)-CH=CH-CH(CH3)-CH2-CH3	2,6-dimethyl	Octene (8C)	2,6-dimethyl-3-octene

Haloalkenes and Haloalkynes: Nomenclature

When halogens are present in alkenes or alkynes:

• Double or triple bonds take precedence over halogen or alkyl groups for numbering.

• Locate the longest chain with the multiple bond first.

• Number from the end nearer the multiple bond.

• List substituents in alphabetical order, with halogens first.

Example:

Structure	Substituents	Parent Chain	IUPAC Name
CH3-C≡C-CH(Br)-CH3	4-bromo	Pentyne (5C)	4-bromo-2-pentyne

Summary Table: Hydrocarbon Types and Nomenclature

Type	General Formula	Bond Type	Example Name
Alkane	$C_nH_{2n+2}$	Single	2,3-dimethylpentane
Alkene	$C_nH_{2n}$	Double	4-methyl-2-pentene
Alkyne	$C_nH_{2n-2}$	Triple	3-methyl-1-butyne
Haloalkane	Varies	Single + Halogen	3-chloro-2-methylpentane
Haloalkene/Haloalkyne	Varies	Double/Triple + Halogen	4-bromo-2-pentyne

Key Nomenclature Rules (IUPAC)

• Identify the longest carbon chain (parent hydrocarbon).

• Number the chain from the end nearest a substituent or multiple bond.

• List substituents (alkyl, halogen) in alphabetical order as prefixes.

• Use prefixes di-, tri-, tetra- for multiple identical substituents.

• Indicate the position of double/triple bonds and substituents with numbers.

Example: For the structure CH3-CH2-C(F)(CH3)-CH2-C(F)-CH2-CH3, the name is 3,5-difluoro-3-methylheptane.

Physical and Chemical Properties

• Hydrocarbons are generally non-polar and insoluble in water.

• They dissolve well in non-polar solvents.

• Boiling and melting points increase with molecular weight.

Additional info:

• These notes cover the foundational nomenclature and classification of hydrocarbons, which is essential for understanding organic chemistry in a general chemistry context.

• Further study may include reactions, isomerism, and aromatic compounds as outlined in the chapter headings.