5. Bonds in organic compound molecules

Alkenes

Hydrocarbons containing at least one carbon-carbon double bond.

Positional Isomerism

Occurs when the position of a functional group (like a double bond) changes along the carbon chain, creating distinct molecules with the same molecular formula.

Positional Isomerism in Alkenes

Ethene (2 carbons) and propene (3 carbons) cannot exhibit positional isomerism. Butene (4 carbons), pentene (5 carbons), and hexene (6 carbons) can exhibit positional isomerism.

Intermolecular Forces (Van der Waals Forces)

Van der Waals Forces

Weak intermolecular forces including London dispersion forces, dipole-dipole interactions, and hydrogen bonds.

Van der Waals Forces in Alkanes

Primary intermolecular forces in alkanes and cycloalkanes are London dispersion forces.

Van der Waals Forces on Physical Properties

Stronger Van der Waals forces lead to higher boiling and melting points due to increased energy required to overcome attractions.

Bonding in Organic Compounds

Single Bonds (Alkanes)

Formed by sp3 hybridized carbon atoms with an ideal bond angle of 109.5° (tetrahedral) when substituents are identical.

Double Bonds (Alkenes)

Formed by sp2 hybridized carbon atoms with a bond angle of approximately 120°.

Triple Bonds (Alkynes)

Formed by sp hybridized carbon atoms with a bond angle of 180° (linear). They are shorter and stronger than double or single carbon-carbon bonds.

Bonds in Benzene

All carbon-carbon bonds are identical in length, intermediate between typical single and double bonds. They are shorter than single bonds and longer than triple bonds.

Polarity of C-I Bonds

Polarity of a bond

Uneven distribution of electron density due to differences in electronegativity between bonded atoms.

C-I Bond Polarity

Generally considered to have lower polarity compared to C-F, C-Cl, or C-Br bonds due to smaller electronegativity difference between C and I. Still polar compared to non-polar bonds.

Reactivity of C-X bonds

C-I bonds are generally more reactive than C-F, C-Cl, or C-Br bonds in nucleophilic substitution due to larger size of iodine making the C-I bond weaker.

Hydrogen Bonds

Hydrogen Bond

Strong dipole-dipole interaction between hydrogen bonded to N, O, or F and another electronegative atom (N, O, F) with a lone pair.

Hydrogen Bond Formation

Requires a hydrogen atom bonded to N, O, or F, and another N, O, or F atom with a lone pair.

Hydrogen Bond Formation

Occurs between water molecules, ethanol and water, formaldehyde and water.

No Hydrogen Bond Formation

Cannot form between water and hydrogen gas (H2) as H2 lacks a hydrogen bonded to an electronegative atom.

Hydrogen Bonds on Solubility

Compounds capable of forming hydrogen bonds with water are generally more soluble in water.

Sulfur Compounds

Sulfonic acids

Contain the -SO3H group; sulfur forms double bonds to two oxygen atoms.

Thiols

Contain the -SH group; sulfur forms single bonds.

Sulfinamides

Contain the -S(=O)NR2 group; sulfur forms one double bond to oxygen.

Sulfonamides

Contain the -SO2NR2 group; sulfur forms two double bonds to oxygen.

Aldehydes and Ketones

Carbonyl Group

The characteristic C=O group in aldehydes and ketones; oxygen has lone pairs, carbon is electrophilic.

Aldehydes and Ketones Reactivity

Susceptible to nucleophilic attack at the carbonyl carbon.

Aldehydes and Ketones Basicity

Generally weaker bases than alcohols due to lone pairs on oxygen being less available for protonation.