Organic Compounds: Aromatic Hydrocarbons and Alcohols – Structure, Naming, and Classification

CHAPTER 11: INTRO TO ORGANIC CHEMISTRY

11.1 Organic Compounds

Organic compounds are molecules primarily composed of carbon and hydrogen, often containing other elements such as oxygen, nitrogen, sulfur, and halogens. They form the basis of organic chemistry and are classified by their functional groups and structural features.

• Key Point: Organic compounds include alkanes, alkenes, alkynes, aromatic hydrocarbons, alcohols, phenols, thiols, and ethers.

• Example: Methane (CH4), Ethanol (CH3CH2OH), Benzene (C6H6).

11.2 Alkanes

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

• Key Point: Alkanes are named according to the number of carbon atoms (methane, ethane, propane, etc.).

• Example: Butane (C4H10).

11.3 Alkanes with Substituents

Substituted alkanes contain additional groups (alkyl, halogen, etc.) attached to the main carbon chain. The position and identity of substituents are indicated in the name.

• Key Point: Number the chain to give the lowest possible numbers to substituents.

• Example: 2-methylpropane.

11.4 Properties of Alkanes

Alkanes are generally nonpolar, insoluble in water, and have relatively low reactivity.

• Key Point: Physical properties depend on molecular size and branching.

11.5 Alkenes and Alkynes

Alkenes contain at least one carbon-carbon double bond ($C=C$), while alkynes contain at least one carbon-carbon triple bond ($C\equiv C$).

• Key Point: The position of the double or triple bond is indicated by numbering the chain.

• Example: 1-butene, 2-butyne.

11.6 Cis-Trans Isomers

Cis-trans (geometric) isomerism occurs in alkenes due to restricted rotation around the double bond, leading to different spatial arrangements of substituents.

• Key Point: Cis isomers have substituents on the same side; trans isomers have them on opposite sides.

11.9 Aromatic Compounds

Aromatic compounds contain conjugated ring systems with delocalized electrons, most commonly exemplified by benzene.

• Key Point: Benzene (C6H6) is a planar, six-membered ring with alternating double bonds (delocalized).

• Example: Toluene, phenol, aniline.

Aromatic Hydrocarbons: Benzene

• Definition: Benzene is the simplest aromatic hydrocarbon, with six carbon atoms joined in a planar hexagonal ring, each bonded to one hydrogen atom.

• Structure:

IUPAC Names: Benzenes

• Key Point: Monosubstituted benzenes are named by indicating the substituent followed by "benzene" (e.g., ethylbenzene, bromobenzene).

• Example:

  Substituent	Structure	Name
  Ethyl	CH2CH3	Ethylbenzene
  Bromo	Br	Bromobenzene

CHAPTER 12: ALCOHOLS

12.1 Alcohols, Phenols, Thiols and Ethers

Alcohols, phenols, thiols, and ethers are organic compounds distinguished by their functional groups.

• Alcohols: Contain a hydroxyl group (-OH) attached to a carbon chain. General formula: $R-OH$.

• Phenols: Contain a hydroxyl group (-OH) attached to a benzene ring.

• Thiols: Contain a thiol group (-SH).

• Ethers: Contain a C-O-C group.

• Functional group: A group of atoms in a molecule with distinctive chemical properties.

Classification Table

Compound	Functional Group	Class
CH3CH2CH3	None	Alkane
OH on benzene ring	-OH	Phenol
CH3CH2OH	-OH	Alcohol
CH3C≡CCH3	C≡C	Alkyne
CH3CH=CH2	C=C	Alkene
CH3CH2SH	-SH	Thiol

12.2 Properties of Alcohols

Alcohols are polar molecules due to the hydroxyl group, which enables hydrogen bonding and increases solubility in water compared to hydrocarbons.

• Key Point: Alcohols have higher boiling points than alkanes of similar molecular weight.

• Example: Methanol (CH3OH) is miscible with water.

Alcohols: Structure

• Alcohol: Organic compound containing a hydroxyl group (-OH) attached to a carbon chain.

• Carbinol carbon: The carbon atom bonded directly to the hydroxyl group.

• General formula: $R-OH$

Alcohols: Naming (IUPAC System)

The IUPAC system names alcohols based on the longest carbon chain containing the -OH group. The suffix -ol replaces the -e of the parent alkane.

• Step 1: Name the longest carbon chain with the -OH group.

• Step 2: Number the chain starting at the end closer to the -OH group.

• Step 3: Name substituents and their positions.

• Step 4: For cyclic alcohols, name as cycloalkanol.

Formula	IUPAC Name
CH4	Methane
CH3OH	Methanol
CH3CH3	Ethane
CH3CH2OH	Ethanol

Examples of Alcohol Naming

• 1-Propanol: $CH_3CH_2CH_2OH$

• 2-Butanol: $CH_3CH(OH)CH_2CH_3$

• 5-Methyl-2-hexanol: $CH_3CH_2CH_2CH(CH_3)CH(OH)CH_3$

Alcohols Naming: Cyclic Alcohols

Cyclic alcohols have an -OH group attached to a cycloalkane ring. The parent compound is named as cycloalkane, and the suffix -ol is added. The carbon with the -OH group is always numbered as C-1.

• Example: Cyclopentanol (5-carbon ring with -OH at C-1)

• Example: 3-methylcyclohexanol (6-carbon ring, -OH at C-1, methyl at C-3)

• Example: 2-ethylcyclopentanol (5-carbon ring, -OH at C-1, ethyl at C-2)

Drawing and Naming Alcohols

• 3-methyl-3-pentanol: Five-carbon chain, methyl and hydroxyl group both at C-3.

• Structure: $CH_3CH_2C(CH_3)(OH)CH_2CH_3$

Practice and Application

Systematic Naming of Aromatic Compounds

• Example: Propylbenzene – benzene ring with a propyl group attached.

Classifying Organic Compounds

• Key Point: Identify the functional group to classify the compound as alkane, alkene, alkyne, alcohol, phenol, or thiol.

Numbering Substituents

• Key Point: When numbering a carbon chain, assign the lowest possible number to the principal functional group or substituent.

• Example: In HC≡C–CH–CH3, the methyl group is at position 3 when numbered from the end closest to the triple bond.

Summary Table: Functional Groups and Classes

Functional Group	Class	Example
-OH	Alcohol	Ethanol
-OH on benzene	Phenol	Phenol
-SH	Thiol	Methanethiol
C-O-C	Ether	Dimethyl ether
C=C	Alkene	Ethene
C≡C	Alkyne	Ethyne

Additional info: These notes cover foundational concepts in organic chemistry relevant to General Chemistry, including structure, nomenclature, and classification of organic compounds, with emphasis on aromatic hydrocarbons and alcohols.