CHEM - Organic part B Flashcards
(31 cards)
When producing an ester, why is heating under reflux and the presence of concentrated sulfuric acid used?
Heating under reflux increases the rate of reaction (at 25 degrees the reaction is slow) as the kinetic energy of the particles is increased and thus more effective collisions occur. Reflux also allows for extended heating without loss of volatile products or reagents. Sulfuric acid acts as a catalyst by providing another energy pathway and thus increases the rate of reaction.
Why are esters less soluble and have a lower boiling point than similar molecular mass alcohols and carboxylic acids?
When formed esters lose the hydroxyl group that both alcohols and carboxylic acids posses. This causes them to lose the ability to hydrogen bond.
What is the general word equation for the production of an ester (esterification)?
Alcohol + carboxylic acid ><(H+) ester + water
If a carboxylate ion has been produced from the hydrolysis of an ester, identify the hydrolysis conditions and suggest a possible reagent.
The production of a carboxylate ion (salt) and an alcohol indicates that hydrolysis was undertaken in acidic conditions. A possible reagent for this may be sodium hydroxide.
If an acid and alcohol are produced, what type of ester hydrolysis has occurred? Also what would be a suitable reagent for this?
Acid hydrolysis has occurred with the use of water and sulphuric acid.
Why is alkaline ester hydrolysis the preferred method?
Alkaline hydrolysis is stronger as it completely forms the products whereas acid hydrolysis is an equilibrium reaction.
An edible oil is a liquid at 25 degrees, what could it have been derived from?
Edible oils are commonly derived from plants and marine animals.
An edible fat is a solid at 25 degrees, what source is it likely to have been derived from?
Solid fats are commonly obtained from land animals.
Why do melting points decrease as the degree of unsaturation in chains increases?
Unsaturated chains (presence of alkene bonds) are less regular compared to saturated chains. This irregularity creates greater distance between the chains, forcing the molecules further apart. Thus the intermolecular dispersion forces are weaker, lowering the melting point.
What are the conditions required for hydrogenation of liquid oils to solid fats?
- increased temperature
- increased pressure
- nickel catalyst
What role does increased temperature play in the hydrogenation of liquid oils to solid fats?
Increased temperature increases the kinetic energy of the reactant particles. In turn increasing the number of productive collisions and hence the rate of the reaction.
What is the role of increased pressure in hydrogenation of liquid oils to solid fats?
Increasing the pressure increases the concentration and therefore the frequency of collisions between reactant particles, in turn increasing the number of productive collisions and hence the rate of the reaction.
What catalyst is used in hydrogenation and what is its role?
A nickel catalyst is used. This catalyst provides an alternative energy pathway got the reaction, with a Lowe activation energy and thus increases the rate of the reaction.
How can the degree of unsaturation in triglycerides be determined by the use of bromine?
- prepare a standard solution of bromine in a suitable organic solvent and add it to the burette
- add known masses of each triglyceride to separate conical flasks
- perform a titration
- fist permanent colour change is the first permanent orange/brown colour that remains after all unsaturated bonds have been broken
- the most unsaturated triglyceride will produce the greater titre value
How is iodine used to determine the degree of un saturation within a triglyceride?
- a titration is performed the same way as with bromine
- except 100g of triglyceride is used in the conical flask
- the mass of iodine required to react with this mass of the triglyceride is known as the iodine number.
What is the amide functional group and is it polar?
FG: NHCO, NCO, CONH2
Polar - ability to form hydrogen bonds
How are amides prepared?
Amides are prepared from the condensation reaction between amines or ammonia and carboxylic acids.
Tertiary amines can’t be used for this as they have no hydrogen present.
What is used for alkaline hydrolysis of amides and what are the products?
- concentrated sodium hydroxide is used for alkaline hydrolysis of amides as amides can only be hydrolysed under strong acidic or alkaline conditions with extended reflux
- the products are a carboxylate salt and either ammonia or an amine
What is used for acid hydrolysis of amines and what are the products?
- concentrated hydrochloride acid is used for acid hydrolysis
- the products are a carboxylic acid and either ammonia or an amine.
How are proteins formed?
Proteins are products of condensation reactions between amino acids. An amino acid molecule contains both a carboxyl and an amino/amine group
Explain zwitterions
Amino acids undergo self ionisation, where a proton is transferred from the carboxyl group to the amine group in the same molecule. Ie.the hydrogen atom dissociates from the carboxyl group and associates with the amino group. The carboxyl group is able to donate a proton as an avid to the amine group to form the protonated amine and carboxylate ion in a neutral pH. This is called a zwitterion.
What are the two main secondary interactions in proteins?
Dispersion forces and hydrogen bonding are the main secondary interactions within proteins.
Most importantly, hydrogen bonding can occur between chains or within a chain, and also between chains and water molecules.
Are proteins soluble in water?
Proteins are not soluble in water. They have lots of opportunities for hydrogen bonding with the amide groups and so are able to absorb water but they are too large to dissolve. Their solubility is similar to polysaccharides.
Why is the structure of proteins important?
The structure of a protein determines it’s function. The biological function of a protein is directly related to its structure. If a protein’s spatial arrangement is altered, it’s biological function is also altered.
