Properties of Alcohols, Aldehydes, Ketones, Amines and Amides

Question 1

Boiling Point: Alcohols

Answer 1

• Higher BP’s than parent Alkanes due to strong hydrogen bonds between alcohol molecules
• BP’s increase with increased chainlength due to more dispersion forces
  BP’s decrease from primarty to tertiary alcochols, increased branching doesn’t stack well therefore weaker dispersion forces.

Question 2

Solubility: Alcohols

Answer 2

-More soluble than parent alkane as OH makes it polar
Soluble as hydrogen bonds form betweem partially positive H atom of hydroxyl group and lone pair electrons of adjacent water molecule

• Less soluble with increased chainlength
• -> Polarity decreased due to increased dispersion forces and net decrease in effect of -OH group which causes alcohol to become less soluble
• -> Reversed effect in organic solvent

Question 3

What are Carboxylic Acids?

Answer 3

• Weak acids as the hydroxyl group can readily ionise and release H+ ions in soltuon, forming conjugate base COO-

Question 4

Boiling Point: Carboxylic Acids

Answer 4

• BP increases as molar mass increases (chain length increase) as dispersion forces increase
• Dimers (circular shape) can form between two carboxylic acids where 2 hydrogen bonds occur between the molecules
• –> Increase in size due to formation of dimer increases strength of dispersion forces between dimers.

Question 5

Solubility: Carboxylic Acids

Answer 5

• Small molecules of Carboxylic acids (up to 4 C) dissolve well in water as they form hydrogen bonds.
• Solubility decreases with increase carbon chain due to increase hdyrophobic interaction of hydrocarbon chain with water.

Question 6

Aldehydes and Ketones General Properties (polarity, intermolecular forces)

Answer 6

-Carbonyl Group (C=O) in both groups is highly polar due to difference in electronegativity of O and C

• Aldehydes and Ketones are Polar Molecules
• Dispersion forces and Dipole-Dipole attractions are the intermolecular forces betwen molecules
• Can’t H bond with each other as no H atoms attached directly to the O

Question 7

Boiling Points: Aldehydes and Ketones

Answer 7

• BP higher than parent alkanes due to dipole-dipole attractions and dispersion forces between the molecules
• Bp increases with increasing chain length due to increased dispersion forces
• Lower BP than similar alcohols as can’t form hydrogen bonds between molecules

Question 8

Solubility: Aldehydes and Ketones

Answer 8

• Solubility decreased with increasing chain length (hydrocarbon’s hydrophobic nature)
• Small Aldehydes and Ketones are soluble in water as they can form hydrogen bonds with the water (between carbonyl oxygen and hydrogen atoms of water)

Question 9

What are Amines?

Answer 9

Weak bases due to long pair of electrons on the N atom

-Uses: Amines are part of amino acids which make up proteins

Question 10

Amines and Amides general Propeties:

Answer 10

• The presence of highly polar N-H covalent bonds in amine and mide molecules mean that these molecules form H bonds
• Strenght of H bonds contributes to high BP of these molecules compared to hydrocarbons of similar size

Question 11

Boiling Point: AMINES

Answer 11

H bonds form between Non-bonding pair of electrons on electronegative N atom and partially positive H atom on another amine molecule

-Amines have lower BP’s than Alcohol as difference in electronegativity between C-N in amines is less than difference in electronegativity between C-O in alcohol.

Question 12

Boiling Points: AMIDES

Answer 12

• Higher BP than amines because they have more atoms that can donate or accept H bonds.
• Strong bonds form bewteen the non-bonding electron pairs on the O atom of one molecule and the positive H atom on a neighbouring molecule

Question 13

Solubility: Amines and Amides

Answer 13

• Small Amines and Amides are soluble in water due to hydrogen bonding between water and Amines and Amides molecules
• Solubility decreases with increasing chain length