LECTURE 8 (Polyfunctional compounds) Flashcards
What are Amines and what are their properties?
Amines contain one or more organic groups bonded to nitrogen in compounds with the general formulas RNH2, R2NH and R3N
PROPERTIES
- Organic derivatives of water
- Classified as primary, secondary or tertiary (according to how many organic groups are individually bonded directly to the nitrogen atom)
- Each amine nitrogen atom has a LONE PAIR OF ELECTRONS -> responsible for chemistry of amines -> fourth group bonds through lone pair, QUATERNARY AMMONIUM ION formed -> permanent +ve charge and forms ionic compounds with anions
What are the properties of the groups bonded to the amine nitrogen atom?
- May be alkyl or aryl groups
- May or may not contain other functional groups
What is NH2?
An amino group
[Aromatic amines are an exception to this rule -> Simplest aromatic amine is called “aniline” and derivates are called anilines]
What does the lone electron pair on the nitrogen amines cause?
It causes amines to act as either WEAK BRONSTED-LOWRY BASES/LEWIS BASES by forming a bond with an H+ ion from an acid or water
What are the boiling point properties of Amines?
- Engage in hydrogen bonding -> primary + secondary amines have higher boiling points than alkanes of similar size
- Lower boiling points than alcohols of similar size
- Tertiary amines have lower boiling points than secondary and primary amines -> Tertiary amines can’t hydrogen bond
What are the properties of Amines?
- Simplest amines are gases, others are liquids
- Volatile amines have unpleasant odours
- Simple amines are water-soluble because of hydrogen bonding with water
- Amines are weak Bronsted-Lowry/Lewis bases
- Many are physiologically active + toxic
What are Heterocycles?
Compounds that contain atoms other than carbon in the ring
Describe the reversible reaction between neutral amines and ammonium ions
- Reversible
- Ammonium ions can react as acids in the presence of bases to regenerate amines
- Equilibrium exists in solution with pH as high as 8
What are Ammonium salts?
Composed of a cation and an anion and are generally odourless, white, crystalline solids that are much more water-soluble than neutral amines since they are ionic
What are Alkaloids?
Roots, leaves and fruits of flowering plants that are a rich source of nitrogen compounds
What is the difference between an Aldehyde and a Ketone?
Aldehyde = carbonyl group is bonded to at least one hydrogen atom so that the -CHO group falls at one end of a molecule
Ketone = carbonyl group is bonded to 2 carbon atoms and is never at the end of the molecule
Describe a carbonyl group
A carbonyl group has a carbon atom and an oxygen atom connected by a double bond
What are the bond angles found between the three substituents on the carbonyl carbon?
120 degrees
Are aldehydes and ketones soluble in organic solvents?
YES
Are aldehydes and ketones soluble in water?
YES - the ones fewer than 5/6 carbons
Explanation: they are able to hydrogen-bond with water molecules but with increasing numbers of carbon atoms, aldehydes and ketones become more alkane-like and less water-soluble
What are the properties of Aldehydes and Ketones?
- Polar due to presence of carbonyl group
- Cannot hydrogen-bond with one another -> lower boiling points than alcohols but higher boiling points than alkanes due to polarity
- Typically liquids
- Simple aldehydes and ketones are water-soluble due to hydrogen bonding with water molecules + ketones are good solvents
- Distinctive odours
Simple ketones are less toxic than simple aldehydes (TRUE/FALSE)
TRUE
What do you get if you oxidise an Aldehyde and a Ketone?
Aldehyde -> Carboxylic acid
Ketone -> No reaction
[since ketones cannot be oxidised, mild oxidising agents are used to distinguish between the two -> TOLLENS’ REAGENT/BENEDICT’S REAGENT]
Describe the reduction of carbonyl groups
Reduction of carbonyl group occurs with the addition of hydrogen across the double bond to produce an -OH group
Aldehydes -> reduced to primary alcohols
Ketones -> reduced to secondary alcohols
What are Carboxylic acids?
Carboxylic acids have an -OH group bonded to the carbonyl carbon atom
What are the derivatives of Carboxylic acids?
- Esters
[have an -OR group bonded to the carbonyl carbon atom] - Amides
[have an -NH2, -NHR or -NR2 group bonded to the carbonyl carbon atom] - Acid anhydrides
[formed when two carboxylic acids join together by eliminating a molecule of water]
Carboxylic acids and their derivatives commonly undergo which reactions?
Carbonyl-group substitution reactions
[A group replaces the group bonded to the carbonyl carbon atom]
What are the properties of Carboxylic acids?
- Behave as weak acids -> surrender hydrogen of COOH to bases and establish acid-base equilibria
- Form hydrogen bonds with each other -> liquid at room temp
What is an Acetyl group?
Acetoic acid losing its “OH” group
Why do Esters have a lower boiling point than carboxylic acids from which they were derived?
When the -OH of the carboxyl group is converted to the -OR of an ester group the ability of the molecules to hydrogen-bond with each other is lost -> simple esters have a lower boiling point than the acids from which they were derived
Do Amides have a higher or lower boiling point than the acids from which they were derived?
Higher
Explanation: Unsaturated amides can form multiple hydrogen bonds to other amide molecules -> higher boiling point than acids from which they were derived
What are the properties of Low-molecular-weight unsubstituted amides?
- Solids
- Soluble in both water and organic solvents
What is the difference between Monosubstituted amides and Disubstituted amides?
Monosubstituted amides = can form hydrogen bonds to each other
Disubstituted amides = cannot hydrogen bond -> lower boiling point
What is the difference between an Amine and an Amide?
The nitrogen atom is bonded to a carbonyl-group carbon in an amide but not in an amine
Explanation: The +ve end of the carbonyl group attracts the unshared pair of electrons on nitrogen strongly enough to prevent it from acting as a base by accepting a hydrogen atom -> Amides are not basic like amines
What are the properties of Carboxylic acids, Esters and Amides?
- All undergo carbonyl-group substitution reactions
- Esters + Amides are made from carboxylic acids and can be converted back
- Carboxylic acids and unsubstituted/monosubstituted amides exhibit strong HYDROGEN BONDING to one another; disubstituted amides and esters do not hydrogen bond to one another
- Simple acids and esters are liquids; all unsubstituted amides are solids
- Carboxylic acids give acidic aqueous solutions; Esters + amides are pH neutral
- Small esters and amides are WATER SOLUBLE
- Volatile acids have strong, sharp odors; volatile esters have pleasant, fruity odours. Amides have no associated odours.
What is Esterification?
Warming a carboxylic acid with an alcohol in the presence of a strong-acid catalyst forming an ester
[Acid-catalysed hydrolysis is a reverse of esterification]
How are unsubstituted and substituted amides formed?
Unsubstituted amides = formed by the reaction of carboxylic acids with ammonia
Substituted amides = produced in reactions between primary and secondary amines and carboxylic acids
Describe ester hydrolysis in the presence of a strong acid catalyst
An ester treated with water in the presence of a strong acid catalyst forms a CARBOXYLIC ACID and an ALCOHOL
[water pushes equilibrium to the right -> more products]
Describe ester hydrolysis in the presence of a base
Called “saponification” forms a CARBOXYLATE ANION and an ALCOHOL
Are amides extremely stable in water?
YES
Explanation: Yes but undergo hydrolysis with heating in the presence of acids or bases -> products are carboxylic acid and amine from which the amide was synthesised
