Alcohols, Amines, and Thiols - Lecture 10

Carbon needs 4 bonds to satisfy the octet rule.
The inner shell has 2 electrons, and the outer valence shell has 4 electrons but desires 8 electrons.
Can form cyclic and aromatic molecules.
Can form alkanes, alkenes, and alkynes

The suffix is used for the highest priority group, while the prefix is used for lower priority groups.
Number of carbons in parent chain:
- 1: Meth-
- 2: Eth-
- 3: Prop-
- 4: But-
- 5: Pent-
- 6: Hex-
- 7: Hept-
- 8: Oct-
- 9: Non-
- 10: Dec-

Alcohols are defined as primary ( $1^{\circ}$ ), secondary ( $2^{\circ}$ ), or tertiary ( $3^{\circ}$ ).
Methanol is used in antifreeze and industrial solvents; added to methylated spirits to make them toxic and cause blindness.
Ethanol is used in alcoholic beverages and as a disinfectant/hand sanitizer.
Oxygen has 6 valence electrons and a -2 charge; it can complete its octet by forming two single bonds or one double bond.

Find the longest carbon chain containing the hydroxyl group.
Derive the parent name, replacing -e with -ol.
Number the carbon chain, giving the hydroxyl group the smallest number.
Number the substituents according to their position on the chain and list them in alphabetical order.
- Name as suffix: -ol.
- Name as prefix: hydroxy.

\textbf{Polarity}: Large electronegativity difference between oxygen and carbon and between oxygen and hydrogen.
- C-O and O-H are polar covalent bonds with partial charges ( $\delta^+$ or $\delta^-$ .
\textbf{Hydrogen Bonding and Boiling Point}:
- H bonding results from the $\delta^+$ on the hydrogen atom and $\delta^-$ on a nearby oxygen atom due to dipole-dipole interactions.
- Alcohols form H bonds with other alcohols and water.
- Boiling point decreases with chain length. Solubility in water increases with shorter chain length.
\textbf{Example}: Methanol vs Hexanol
- Methanol: Hydrophilic, infinite solubility, boiling point 65°C.
- Hexanol: Hydrophobic, slightly soluble, boiling point 157°C.

Amines are derivatives of ammonia ( $NH_3$ ) with one or more H atoms replaced by alkyl or aryl groups.
Classified as primary, secondary, or tertiary depending on the degree of substitution on the nitrogen atom.
Amine groups are found in biologically active molecules like drugs such as cocaine, nicotine and methamphetamine.

Find the longest carbon chain containing the amine group.
Derive the parent name, replace -e with –amine
Number the carbon chain numbering the amine group with the smallest number
Number the substituents according to their position on the chain, and write the name, listing the substituents in alphabetical order and identifying the position to which the N is bonded.
- Name as suffix: –amine
- Name as prefix amino

Amines are polar compounds that can form hydrogen bonds.
Tertiary amines cannot form H bonds with themselves, but they can with water.
N-H…N hydrogen bond is weaker than an O-H…O hydrogen bond because oxygen is more electronegative than nitrogen.
\textbf{Boiling point}: Amines have higher boiling points than alkanes with similar molecular weight but less than alcohols, due to H bonds with water.
- Boiling point increases: tertiary < secondary < primary.
\textbf{Solubility}: Small amines are very soluble in water; amines with more than 6 carbons have lower solubility.

Sulfur analogues of alcohols with SH bonded to an $sp^3$ hybridized carbon atom.
Sulfur and oxygen belong to the same group in the periodic table, so thiols and alcohols have similar properties.

Find the longest carbon chain containing the thiol group.
Derive the parent name and add –thiol to the name of the parent chain if it is the only functional group.
Number the carbon chain, numbering the thiol group with the smallest number.
Number the substituents according to their position on the chain, and write the name, listing the substituents in alphabetical order and identifying the position to which the thiol is bonded.
- Name as suffix: -thiol
- Name as prefix: Sulfanyl (mercapto is still used elsewhere)

\textbf{Polarity}: Small difference between the electronegativity of sulfur and carbon and between sulfur and hydrogen.
S-C and S-H are non-polar covalent bonds with no partial charge.
Thiols do not form hydrogen bonds or dipole-dipole interactions but have dispersion (London) forces.
Thiols have lower boiling points than similar alcohols and are less soluble in water than alcohols of comparable molecular weight.
Low molecular weight thiols have a strong odor and are volatile; used as natural gas odorants.

Intermolecular forces: ionic bonding > H bonding > dipole-dipole > Van der Waals/London dispersion forces.
Pauling scale quantifies electronegativity; the magnitude of difference determines polarity.

\textbf{Functional Group}:
- Alkanes: Van der Waals.
- Alcohols: H bonding with itself and water, Van der Waals, dipole-dipole.
- Amines: H bonding with itself and water, Van der Waals, dipole-dipole.
- Thiols: Van der Waals.
\textbf{Exceptions}: Branched chains have lower boiling points; as chain length increases, H bonding is less; tertiary amines do not H bond; thiols do not H bond with themselves (low polarity).
Boiling point trend: primary > secondary > tertiary due to the availability of Hydrogens and less steric bulk.
Boiling point increases with molecular weight and surface area.
Straight-chain molecules have a higher boiling point than branched molecules of the same size.