✅17 - Organic Chemistry II Flashcards
What type of isomerism is optical isomerism?
Stereoisomerism
What are structural isomers?
Compounds with the same molecular formula but with different structural formula
What are functional group isomers?
They differ because they have different functional groups
What are chain isomers?
Differ because they have different patterns of branching in their carbon chains
What are positional isomers?
Differ because the same functional group is attached to different carbon atoms in the chain
What are stereoisomers?
Have the same structural formula but differ because their atoms or groups are arranged differently in three dimensions
What are geometric isomers?
type of stereoisomer with the same molecular formula and connectivity but different spatial arrangement.
What is chirality?
Two or more molecules that appear identical but cannot be superimposed onto one another.
What are chiral centres?
Carbons with four different atoms or groups attached
What is plane polarised light?
light that vibrates in one direction only
Do enantiomers have identical physical properties?
Yes, except in optical rotations where one rotates clockwise and the other does not
Do enantiomers have identical chemical properties?
yes, especially with non-chiral substances but may behave differently with other chiral molecules.
important for biological molecules such as enzymes.
e.g ibuprofen- 1 enantiomer is active, the other isnt active
What is a racemic mixture?
One containing equal amounts of two enantiomers.
What does SN2 indicate?
S = substitution N= nucleophillic 2=bimolecular and second order
Bimolecular means that the rate is determined by the 2 species, both the nucleophile and the substrate.
What does SN1 indicate?
S = Substitution N = Nicleophillic 1 = unimolecular and first order
How can optical activity be used as evidence for SN2?
In an SN2 reaction, the nucleophile attacks the carbon atom where the leaving group is attached, and simultaneously the leaving group departs. This leads to an inversion of configuration—the chiral center of the molecule flips, meaning if it was originally “left-handed” (L), it becomes “right-handed” (R), or vice versa.
this confirms sn2 has taken place.
How can optical activity be used as evidence for SN1 mechanisms?
If the reaction is via SN1, there will be no optical activity in the product.
What is a carbonyl group?
C=O
What compounds are classified as carbonyl compounds?
Aldehydes and Ketones
What defines an aldehyde?
A hydrogen joined to a carbonyl group
What defines a ketone?
If there are only hydrocarbon groups joined to the carbonyl
How do carbonyl groups affect bonding?
They form polar bonds, because oxygen is much more electronegative than carbon
What are the physical properties on aldehydes?
Boiling Point: Moderate, higher than alkanes, lower than alcohols.
Solubility: Small aldehydes are water-soluble; larger ones are not.
Odor: Often pungent, with some (e.g., vanillin) being pleasant.
Polarity: Polar due to the carbonyl group.
Reactivity: More reactive than ketones due to the carbonyl group.
What are the relative boiling points of aldehydes, ketones, alcohols and alkanes?
Alkanes < Aldehydes < Ketones < Alcohols
Why do aldehydes and ketones have lower boiling points than alcohols?
They have intermediate intermolecular forces, only dipole dipole, so hydrogen bonds are not able to form because all the hydrogen atoms are attached to carbon atoms only.
How soluble are aldehydes and ketones?
Smaller aldehydes and ketones are soluble because they can form hydrogen bonds with water. Solubility decreases with chain length
What can aldehydes and ketones be reduced to?
Alcohols
What is the reagent for reduction of aldehydes and ketones?
Lithium Aluminium Hydride
How are reductions of carbonyl compounds carried out?
With both the carbonyl and reducing agent in dry ether
What reagents can be used to oxides aldehydes to carboxylic acids?
Acidified potassium dichromate, Fehling’s, Benedict’s, Tollens’
What is the colour change for acidified potassium dichromate?
Orange —-> green
What is the colour change for Fehling’s?
Deep blue solution —-> red precipitate
What is the colour change for Benedict’s?
Deep blue solution —-> red precipitate
What is the colour change for Tollens’?
Colourless solution —-> Silver mirror
How can you distinguish between aldehydes and ketones?
Aldehydes react with Benedict’s, Fehling’s and Tollens’, ketones do not
How do aldehydes and ketones react with iodine?
Carbonyls with CH3CO react with iodine to for triiodomethane - a yellow precipitate
What is the equation for the reaction between a carbonyl compound and iodine?
COCH3 + 3I2 + 4OH- ——> RCOO- + CHI3 + 3I- + 3H20
How can Brady’s reagent be used to distinguish between aldehydes and ketones?
An orange precipitate forms if a carbonyl is present
The precipitate can be purified by re-crystallisation
Each different carbonyl give a crystal with a different melting point
If the melting points are measured and compared to a table of known values, the compound can be identified
Under what conditions do reactions with hydrogen cyanide occur?
In aqueous alkaline solution containing potassium cyanide
What is the equation for addition of HCN to propanal?
CH3CH2CHO + HCN —-> CH3CH3CH(OH)CN
What is the equation for addition of HCN to butanone?
CH3COCH2CH3 + HCN —-> CH3C(CN)(OH)CH2CH3
What type of mechanism is the addition of hydrogen cyanide to a carbonyl?
Nucleophilic addition
What does the addition of HCN involve?
The hydrogen atom attaches to the oxygen of the carbonyl and a cyanide group attaches to the carbon of the carbonyl group
How many steps are in the nucleophillic addition of HCN?
Two , and an intermediate is formed
How can optical activity be used as evidence for the mechanism of addition of HCN?
The arrangement of the two atoms or groups attached to the C=O is planar, so the cyanide ion can attack from above or below. Creates a chiral carbon, but with a equal amounts of dextrorotatory and laevorotatory enantiomers, no optical activity.
What is the common name for methanoic acid?
Formic acid
How is the charge distributed in a carboxylate (COO-) ion?
Evenly
What are the physical properties of carboxylic acids?
They have distinctive smells and sour tastes
What are the relative boiling points for carboxylic acids?
Very high
Why do carboxylic acids have high boiling points?
They have three polar bonds in the carboxylic acid group which give them strong intermolecular forces and hydrogen bonding
How does the length of the carbon chain in a carboxylic acid affect the boiling point?
The longer the chain, the higher the boiling point because London forces increase
Why do shorter carboxylic acids form dimers?
In the absence of a solvent, two molecules hydrogen bond with one another
What type of carboxylic acids are soluble in water?
Shorter chain ones, as they can form hydrogen bonds with water
How does chain length affect solubility in carboxylic acids?
Solubility decreases with increasing chain length
What are the two main methods of producing carboxylic acids?
Oxidation and hydrolysis
What are the conditions for oxidation of a primary alcohol or aldehyde to form a carboxylic acid?
Acidified potassium dichromate (VI) and reflux
What is the equation for the oxidation of propan-1-ol to propanoic acid?
CH3CH2CH2OH + 2[O] —-> CH3CH2COOH + H20
What is the equation for the oxidation of propanone to propanoic acid?
CH3CH2CHO + [O] —-> CH3CH2COOH
What can be hydrolysed to from a carboxylic acid?
Nitriles and organic compounds containing CN group
What are the conditions for hydrolysing nitriles to form carboxylic acids?
Reflux with either a dilute acid or aqueous alkali
What is the equation for the hydrolysis of propanenitrile with dilute acid?
CH3CH2CN + H+ + 2H2O —-> CH3CH2COOH + NH4+
What is the equation for the hydrolysis of butanenitrile with aqueous alkali?
CH3CH2CH2CN + OH- + H2O —-> CH3CH2CH2COO- + NH3
Butanoate ion then converted into acid by adding dilute acid:
CH3CH2CH2COO- + H+ —-> CH3CH2CH2COOH
What are the four main reactions of carboxylic acids?
Reduction
Neutralisation
Halogenation
Esterification
What is the product of neutralisation of a carboxylic acid?
A carboxylate salt
Which reducing agent is used to reduce carboxylic acids?
Lithium aluminium hydride
What is the equation for the neutralisation of ethanoic acid using sodium hydroxide?
CH3COOH + NaOH —-> CH3COONa + H2O
What is the product of halogenation of a carboxylic acid?
Acyl chloride
What are the conditions for halogenation of carboxylic acids?
Phosphorus (V) chloride and anhydrous conditions
Why are anhydrous conditions used for halogenation of carboxylic acids?
Because both the reagent and the acyl chloride react vigorously with water
What is the equation for the halogenation of propanoic acid?
CH3CH2COOH + PCl5 —-> CH3CH2COCl + POCl3 + HCl
What are the conditions for esterification of carboxylic acids?
Alcohol and a small amount of acid catalyst, often conc H2SO4
What is the equation for the esterification of mathanoic acid with ethanol?
HCOOH + CH3CH2OH HCOOCH2CH3 + H2O
What is the general formula for acyl chlorides?
RCOCl
What are acyl chlorides prone to?
Nucleophillic attack, as the carbon is joined to two electronegative atoms, so is electron deficient
How do acyl chlorides react with cold water?
Vigorously, forming a carboxylic acid and releasing hydrogen chloride gas, appearing as misty fumes
What is the equation for the reaction of ethanoyl chloride and water?
CH3COCl + H2O —-> CH3COOH + HCl
How do acyl chlorides react with alcohols?
They readily react with ethanol to form ab ester and hydrogen chloride gas
What is the equation for the reaction of ethanoyl chloride with ethanol?
CH3COCl + CH3CH2OH —-> CH3COOCH2CH3 + HCl
How do acyl chlorides react with concentrated ammonia solution?
In two steps, an NH2 group joins with the carbonyl group to produce an amide as well as ammonium chloride
What is the equation for the reaction between ethanoyl chloride and conc ammonia?
CH3COCl + 2NH3 —-> CH3CONH2 + NH4Cl
How do acyl chlorides react with primary amines?
One H form the amine react with Cl to form HCl and the rest of the compound is attached to the carbonyl group
What is the equation for the reaction between ethanoyl chloride and methylamine?
CH3COCl + CH3NH2 —-> CH3CONHCH3 + HCl
Why don’y acyl chlorides react with tertiary amines?
There is no H to react with the Cl to form HCl
What are the physical properties of esters?
Colourless liquids with low melting and boiling points, insoluble in water, no hydrogen bonding. Generally pleasant smell.
What are the two types of hydrolysis of esters?
Hydrolysis in acidic solution and in alkaline solution
What is the equation for hydrolysis of ethyl ethanoate with a sulfuric acid catalyst?
CH3COOCH2CH3 + H2O CH3COOH + CH3CH2OH
What is the equation for the hydrolysis of methyl propanoate in alkaline solution?
CH3CH3COOCH3 +NaOH —> CH3CH2COO- + Na+ + CH3OH
What is saponification?
Alkaline hydrolysis of esters to form an alcohol and a stearate, commonly used in soaps
What is condensation polymerisation?
Each time two monomer molecules join together, another small molecule is formed
Usually two different monomers react together
What is the small molecule formed during condensation polymerisation?
Often water
How are polyesters formed?
Through condensation polymerisation
What are the monomers of polyesters?
A diol and a dicarboxylic acid
