isomerism and carbonyl compounds

name the six functional groups of carbonyl compounds

•ester 

•aldehide

•ketone

•carboxylic acide

•acyl chloride 

•acid anhydride

define aldehydes and ketones

compounds that both contain carbonyl group (C=O) as their functional group, with aldehydes having the carbonyl group at the end of a carbon chain and ketones having it within the chain.

define a neucliophile

an electron-rich species that donates a pair of electrons to form a chemical bond with an electron deficient species.

define electrophile

an electrophile is an electron acceptor species that accepts electrons to form a chemical bond.

functional group and nomenclature for an ester

•Esters are formed from a condensation reaction between a carboxylic acid and an alcohol, producing a molecule of water. the H is from the alcohol and OH from carboxylic acid.

•prefix is the alcohol

•suffix is the carboxylic acid.

• example-

• Ester: CH₃COOCH₂CH₃

• Alcohol part: From ethanol (CH₃CH₂OH), which becomes ethyl.

• Acid part: From ethanoic acid (CH₃COOH), which becomes ethanoate.

• Full Name: Ethyl ethanoate

functional group and nomenclature for amides

suffix- amide

functional group and nomenclature for acyl chlorides

suffix- oyl chloride

•drop the -oic acid from the parent carboxylic acid and replace with -oyl chloride

what is a chiral carbon?

•A chiral carbon is a carbon atom with four different atoms or groups of atoms attached to it.

•creates a tetrahedral structure.

•has optical isomers

define optical isomer. how can they be distinguished?

•optical isomerism describes stereoisomers that are non-superimposable mirror images of each other, like left and right hands.

•These molecules, called enantiomers, possess the same molecular formula and bonding but differ in their three-dimensional arrangement due to a chiral carbon (a carbon atom bonded to four different groups).

•Optical isomers have the same physical properties but rotate plane-polarized light in opposite directions, a property that distinguishes them.  

what is the structural feature of optical isomers that makes them isomers?

they are non super imposable mirror images

define a racemic mixture

a solution containing an equal mixture of enantiomers

how is plane polarised light made? (Diagram) how does this enable us to distinguish enantiomers?

•when plane polarised light is passed through separate solutions of enantiomers, they rotate the light in equal and opposite directions

what happens when plane polarised light is passed through a racemic mixture?

•when plane polarised light is passed through a racemic mixture of equally mixed enantiomers, they will appear inactive.

•this is because the effects of one isomer cancels out the other.

why do we get a racemic mixture with KCN/H2SO4 and NaBH4. explain why the product has no effect on plane polarised light 

• the planer carbonyl group is equally likely to be attacked above or below its plane

• this leads to equal quantity’s of both enantiomers being formed (racemic mixture)

• one isomer will rotate plane polarised light clockwise and the other, anticlockwise , so effects will cancel out. 

what reagents can distinguish between aldehydes and ketones

•using weak oxidising agents such as…

•Tollens reagent (ammoniacal silver nitrate [(AgNH3)2]+. if aldehyde present a silver mirror precipitate will appear as silver atoms reduced.

•Fehlings solution- Cu2+ oxidised to Cu+. if aldehide present will go from blue to brick red precipitate.

what reaction mechanism is used to form hydroxy nitriles

nucleophilic addition

what functional groups form hydroxy nitriles?

aldehydes and ketones

what reagents are used in nucleophilic addition? what is the alternative reagent and why is this not used commercially?

• Potassium cyanide/ KCN

• Followed by H2SO4

• HCN- very toxic 

Diagram - reaction mechanism to form hydroxy nitriles 

what is the prefix for hydroxy nitriles and why isn’t there a suffix typically

Prefix- Cyano

• always highest priority apart from in the presence of a carboxylic acid group

what is the mechanism for the reduction of aldehydes and ketones. state the reagent and products.

• nucleophilic addition 

• sodium borohydride solution (NaBH4)

• aldehyde+2[H]—→ Primary alcohol

• ketone+2[H]—> secondary alcohol 

diagram of the mechanism 

• ignore the OH on the water and in the products. mechanism only needs H- as nucleophile 

what are the two acceptations of an aldehyde and ketone where a racemic mixture isn’t formed?

• methanal- no chiral carbon

• symmetrical ketones- no chiral carbon

what 3 reactions do acids do?

• acid + base—> salt + water

• acid + metal —> salt + H2

• acid + metal carbonate —> salt + CO2 +H2O (test for carboxylic acid)

why are carboxylic acids not strong acids?

• not many H+ ions will dissociate

• use reversable reaction arrows

the acid + base reaction of ethanoic acid (CH3COOH) and sodium hydroxide (NaOH)

• CH3COOH +NaOH —→ CH3COONa + H2O

the acid + metal carbonate reaction between ethanoic acid (CH3COOH) and sodium hydrogen carbonate (NaHCO3).

Give an observation and use for this reaction. 

• 2CH3COOH + NaHCO3 —>2CH3COONa + H2O + CO2

• observation- effervescence 

• use- to test for carboxylic acid

the acid + metal reaction between ethanoic acid (CH3COOH) and magnesium (Mg)

2CH3COOH + Mg -→ (CH3COO-)2 Mg2+ +H2

Why is these reaction unusual?

unusual to have ionic interactions within a covalent molecule

What reaction with carboxylic acid forms an ester? what catalyses this reaction?

carboxylic acid + alcohol —> ester + H2O

• concentrated H2SO4

where between the two molecules does an ester bond form?

OH group of carboxylic acid and the H of alcohol

describe briefly how you could measure the melting point of aspirin. how can you tell if its pure?

Method-

• put sample in capillary tube

• heat rapidly until it gets close to melting point and then heat slowly once close so you don’t miss the point at which it starts melting

• record temp that it first starts melting and the temperature at which all the substance is melted

How to tell if its pure-

• the closer the melting point to that of pure aspirin, the closer it is to being pure 

• the smaller the range between start and end melting point, the closer it is to pure aspirin.

what is the general equation for esterification ?

acid + alcohol —c.H2SO4→ ester + water 

What are the conditions and catalyst for esterification ?

concentrated H2SO4 reflux

how are esters named

• prefix- alcohol

• suffix- carboxylic acid

• conditions, products and reagents for base hydrolysis of esters

• what happens if you further react with HCL?

• dilute NaOH

• reflux

• produces sodium salt of carboxylic acid and alcohol

• remove the Na and produce original carboxylic acid

• conditions, products and reagents for acid hydrolysis of esters

• reflux 

• H2O + acid catalyst

• produces carboxylic acid and alcohol

is acid or base hydrolysis preferred and why ?

• base hydrolysis

• acid hydrolysis is a reversible reaction so low yield

• base hydrolysis is also a faster reaction

Oils and fats (triglycerides) are esters made from …

• sodium salts of long chain carboxylic acids

• glycerol

how are triglycerides hydrolysed and what are the products? name this reaction 

• hydrolysed by 3NaOH under reflux

• form 3 sodium salts of long chain carboxylic acid

• and glycerol 

• saponification 

what are the products of saponification used for?

• sodium salts of carboxylic acids used to make salts 

• glycerol is a good organic solvent- eg acetone

how Is biodiesel formed? name this process.(what do you react with triglycerides and are the products ?)

• transesterification

• react with 3 molecules of methanol under reflux with KOH catalyst

• forms methyl esters of long chain carboxylic acids and glycerol as a waste product

what is biodiesel a mixture of ?

methyl esters

what is the test reagent and observation for acyl chlorides

reagent- H2O

observation- white fumes

what is the mechanism when nucleophiles react with acyl chlorides ?

nucleophilic addition elimination 

give the nucleophiles that react with acyl chlorides and products

• NH3- amide +HCL

• R-OH- ester + HCL

• R-NH2- N-substituted amide + HCl

• H2O- carboxylic acid + HCl

reaction conditions and observation for nucleophilic addition elimination of acyl chlorides

• anhydrous conditions unless using H2O

• white fumes, vigorous reaction

disadvantage of acyl chloride reactions

produce toxic HCL gas

what are the industrial advantages and disadvantages of acid anhydrides and acyl chlorides in the manufacture of aspirin?

acyl chlorides-

advantages

• very reactive

disadvantages

• produces corrosive HCL gas

• difficult to handle

acid anhydride-

advantages

• cheeper to produce

• less corrosive

• makes carboxylic acid instead of HCL gas

disadvantages

• slower reaction

what 4 nucleophiles react with acid anhydrides during nucleophilic addition elimination? What are the products formed? 

• H2O- 2x carboxylic acid 

• R-NH2- N-substituted amide + carboxylic acid

• NH3- amide + carboxylic acid 

• R-OH- carboxylic acid + ester 

what is an acid anhydride and how are they named?

• formed from condensation reaction of 2 carboxylic acids and produce a molecule of water

• suffix- oic anhydride

• symmetrical- the name is based on the single parent acid (e.g., ethanoic acid becomes ethanoic anhydride)

• asymmetrical- formed from two different acids, the names of both parent acids are listed before the word "anhydride," separated by a space (e.g., ethanoic propanoic anhydride). 

  
  

define a condensation reaction

the joining of two molecules to form a larger molecule, with the elimination of a smaller molecule (eg water)