Organic Molecule Structure & Properties

• Organic chemistry involves the study of carbon compounds.

Homologous Series

• A group of organic compounds share the same general formula and functional group.
• These compounds' members differ by a CH2 group.

General Formula

• It is a formula to determine a molecular formula of any member in a homologous series.
• Alkanes, can be described by CnH2n + 2
• An alkane with 100 carbon atoms will have a molecular formula of C100H202.

Functional Group

• A bond, atom, or group of atoms determines the physical and chemical properties of organic compounds.

Molecular Formula

• It is a chemical formula that indicates the type and number of atoms in a molecule.
• For example: C3H8

Condensed Structural Formula

• Illustrates how atoms bond together, without showing all bond lines
• For example: CH3CH2CH3

Structural Formula

• Shows which atoms are attached to which by using chemical symbols for atoms and lines for all bonds.
• Structural formulas do not usually depict the actual geometry/shape of molecules.

Isomerism

• The organic molecules have a molecular formula that corresponds with that of another molecule.

Structural Isomers

• These are compounds that share a molecular formula but have different structural formulas.

Hydrocarbons

• These compounds consist of carbon and hydrogen atoms only.

Substituent

• A group/branch is attached to the longest continuous chain of carbon atoms in an organic compound.

Alkanes

• Alkanes are organic compounds containing only C-H and C-C single bonds with a general formula of CnH2n + 2.

Saturated Hydrocarbons

• Saturated hydrocarbons contain only C-H and C-C single bonds, containing the maximum number of hydrogen atoms per carbon.
• Saturated hydrocarbons have no multiple (double or triple) bonds.

Unsaturated Hydrocarbons

• These hydrocarbons contain carbon-carbon double bonds.
• They do not contain the maximum number of hydrogen atoms per carbon.

Alkyl Group

• Formed by removing one H atom from an alkane.

Cycloalkanes

• Organic compounds contain carbon and hydrogen, bonding carbon atoms in rings with single bonds only, and have the general formula CnH2n.

Alkene

• A compound of carbon and hydrogen contains a carbon-carbon double bond, described by the general formula CnH2n.

Cycloalkene

• A compound of carbon and hydrogen bonds carbon atoms in a ring containing one double bond
• Given by the general formula: CnH2n - 2

Diene

• A compound has two carbon-carbon double bonds
• Given by formula CnH2n - 2

Alkyne

• A compound has one carbon-carbon triple bond
• Given by formula: CnH2n – 2

Haloalkane

• A haloalkane (or alkyl halide) is an organic compound where one or more H atoms in an alkane have been replaced with halogen atoms
• Described by formula: CnH2n + 1X (X = F, Cl, Br or I)

Primary Haloalkane

• A primary haloalkane is one C atom bonded to the carbon bonded to the halogen.

Secondary Haloalkane

• A secondary haloalkane is two C atoms bonded to the carbon bonded to the halogen.

Tertiary Haloalkane

• A tertiary haloalkane is three C atoms bonded to the carbon bonded to the halogen.

Alcohol

• Alcohols are organic compounds that have -OH (hydroxyl) groups substituted for H atoms in an alkane
• General formula: CnH2n + 1OH

Primary Alcohol

• A primary alcohol has one carbon atom bonded to the carbon bonded to the hydroxyl group.

Secondary Alcohol

• A secondary alcohol has two carbon atoms bonded to the carbon bonded to the hydroxyl group

Tertiary Alcohol

• A tertiary alcohol has three carbon atoms bonded to the carbon that is bonded to the hydroxyl group

Aldehydes

• These are organic compounds that have the general structure RCHO where R = H or alkyl. The general formula is RCHO (R = alkyl group).

Carboxyl Group

• The functional group of carboxylic acids (-COOH)

Carbonyl Group

• Functional group of ketones (>C=O).

Boiling Point

• The temperature at which the vapor pressure of a liquid equals atmospheric pressure or external pressure occurs.

Melting Point

• The temperature at which a solid changes to a liquid phase.

Viscosity

• The resistance of a fluid (liquid or gas) to flow
• A greater a fluid's viscosity means the more slowly it flows.

Vapour Pressure

• The pressure at which the vapor of a substance is in dynamic equilibrium with its liquid or solid form.
• Substances with high vapor pressure are volatile and have volatility.

Substitution Reaction

• This is where an atom or group of atoms in a molecule is replaced by another atom or group of atoms.

Elimination Reaction

• A reaction in which elements of the starting material are “lost” and a double bond forms.

Addition Reaction

• A double bond in the starting material is broken and elements are added to it.

Halogenation

• Halogenation is the reaction of a compound with a halogen (Br2, Cl2, I2, F2).

Cracking

• Cracking is the break-up of molecules with a large molecular mass into molecules with smaller molecular masses.

Hydrogenation

• The addition of hydrogen to a molecule.

Hydrohalogenation

• The addition of a hydrogen halide (HX) to a molecule.

Hydration

• Hydration is the addition of water to a molecule.

Dehydrohalogenation

• Is the elimination in which hydrogen and a halogen are lost from a molecule.

Dehydration

• Dehydration is the removal of water from a molecule.

Esterification

• Esterification is the preparation of an ester from the reaction of a carboxylic acid with an alcohol.

Functional Groups of Organic Compounds

• Alkanes contains C-H and C-C single bonds, such as ethane.
• Alkenes contain C=C bonds, for example, ethene.
• Alkynes contain -C≡C- bonds, an illustration is ethyne.
• Haloalkanes (alkyl halides) contain C-X bonds where (X = F, Cl, Br, I), an example is bromoethane.
• Alcohols (alkanols) contain -O-H bonds, such as ethanol.
• Aldehydes contain a carbonyl group (C=O) bonded to at least one hydrogen atom, such as ethanal.
• Ketones feature a carbonyl group (C=O) bonded to two carbon atoms like propan-2-one
• Carboxylic acids contain a carboxyl group (-C(=O)OH), such as ethanoic acid.
• Esters are compounds with the structure R-C(=O)O-R', methyl ethanoate is an example.

Naming Organic Compounds

• Every organic molecules' name has three parts:
  • A parent name indicates the number of C atoms in the longest carbon chain in the molecule.
  • A suffix indicates what functional group is present.
  • A prefix reveals the identity, location, and number of substituents attached to the carbon chain.

Physical Properties of Organic Compounds

• Compounds with high boiling points have low vapor pressures.
• Physical properties of compounds depend on the strength of intermolecular forces (forces between molecules).
• Stronger intermolecular forces result in higher boiling points, melting points, viscosities, and lower vapor pressures.

Types of Intermolecular Forces

• Strong hydrogen bonds only occur between molecules where H is covalently bonded to a N, O, or F atom between molecules of alcohols and carboxylic acids.
• Weak Van der Waals forces exist between all molecules. This force is stronger between polar molecules than non-polar.

Relationship between boiling point / melting point / viscosity / vapour pressure and chain length

• Increasing the chain length increases molecules surface area, increasing strength of intermolecular forces, thereby, increasing boiling point / melting point / viscosity, but decreasing vapour pressure

Relationship between boiling point /vapour pressure and Branching

• Increasing branching decreases molecules surface area, decreasing strength of intermolecular forces and decreasing boiling point. As such, vapour pressure increases.

Relationship between boiling point / melting point / viscosity and TYPE OF FUNCTIONAL GROUP

• With increasing polarity of the functional group, and increasing strength of intermolecular forces, there is an increase in boiling point, melting point and viscosity.
• There is a decrease in vapor pressure.

This module explores the correlation between organic molecule structures and their names, including prefixes, parent chains, and suffixes. We will investigate how intermolecular forces affect boiling points, melting points, vapor pressure, and viscosity. Chain length and branching effects on physical properties are also discussed.