Organic Chemistry: Carbon Bonds and Formulas

• Organic chemistry is the study of carbon compounds, with the exception of a few simple inorganic compounds; all organic compounds contain carbon
• Carbon can form a huge number of compounds because carbon atoms can bond to each other and form stable chains (catenation)
• Carbon atoms form strong covalent bonds with each other and have no free valence electron pairs or orbitals and are four-bonded
• Carbon has a favorable electronegativity value to create chains
• Carbon belongs to group 14, period 2, and has an atomic number of 6

Position of Double Bonds

• Isolated double bonds are separated by at least one single bond: C=C-C-C=C
• Conjugated double bonds alternate single and double bonds: C=C-C=C
• Cumulative double bonds have double bonds next to each other: C=C=C

Number of Bonds

• Carbon: 4 (tetravalent)
• Hydrogen: 1 (monovalent)
• Oxygen: 2 (divalent)
• Sulfur: 2 (divalent)
• Nitrogen: 3 (trivalent)
• Halogens: 1 (monovalent)

Formulas in Organic Chemistry

• Molecular Formula: C4H8O2
• Empirical Formula: C2H4O
• Condensed Formula: CH3CH2CH2COOH
• Displayed Formula: Shows all atoms and bonds
• Structural Formula: CH3-CH2-CH2-COH
• Skeletal Formula: Shows only the carbon skeleton and functional groups

Isomerism

• Isomers are molecules with the same molecular formula but different structures (arrangement of atoms)

Structural Isomers

• Chain isomers have different arrangements of the carbon chain, example C5H12, CH3-CH2-CH2-CH2-CH3 or CH3-CH(CH3)-CH2-CH3
• Positional isomers differ in the position of a functional group or multiple bond, example C4H8 and multiple bond placement or C5H11Cl and different chloride position on pentane
• Functional isomers have different functional groups, example C3H8O, CH3-CH2-CH2-OH (alcohol) or CH3-O-CH2-CH3 (ether)

Stereoisomerism

• Geometric isomers exist in compounds with a double bond where rotation is restricted; cis-but-2-ene and trans-but-2-ene
• Optical isomers are optically active, rotating polarized light
• Conformational isomers can rotate around a single bond; eclipsed and staggered conformations

Reactions of Organic Compounds

• Organic reactions are slower compared to inorganic reactions
• Most organic reactions only occur at high temperatures and in the presence of a catalyst
• Saturated hydrocarbon reactions occur on C-C or C-H bonds
• Unsaturated hydrocarbon reactions occur on the multiple bond
• Hydrocarbon derivative reactions occur on the functional group
• Organic reactions happen through multiple steps; the detailed description of these steps is called the reaction mechanism
• The simplified version is called the reaction scheme
• Substrate: the reactant on which the change happens
• Reagent: the reactant that causes the change, typically small inorganic molecules

Classification of Organic Compounds

Hydrocarbons

• Contain only carbon and hydrogen

Hydrocarbon Derivatives

• Created by substituting one or more hydrogen atoms in the hydrocarbon molecule with a functional group

Division of Organic Compounds

According to the Nature of the Carbon Chain

• Acyclic: branched or unbranched
• Cyclic: have a closed chain

According to Type of Bond

• Saturated: contain only single bonds
• Unsaturated: contain multiple bonds
• Aromatic: contain an aromatic core
• Aliphatic: saturated or unsaturated

Further Noteworthy Points

• Catenation is the ability of carbon atoms to bond to each other and form stable chains
• Homolytic reactions: bond fission is symmetrical, forming radicals
• Heterolytic reactions: bond fission is asymmetrical, typical for polar compounds, forming ions

Types of Reagents

• Radical reaction with radicals (particles with unpaired electrons)
• Electrophilic reaction with electrophiles (particles that attract electrons)
• Nucleophilic reaction with nucleophiles (particles with available electrons)

Nature of Change on the Substrate

• Addition, typical for unsaturated compounds
• Elimination, opposite of addition, small molecule is eliminated
• Substitution, one atom or group is replaced by another
• Molecular rearrangement, atoms are rearranged within the same molecule

Nomenclature of Organic Compounds

• Aliphatic hydrocarbons can be saturated (alkane), unsaturated (alkene, alkyne)
• Cyclic hydrocarbons can be cycloalkanes, cycloalkenes, cycloalkynes