Organic chem

Question 1

define the term meso compound

Answer 1

a type of stereoisomer
has multiple chiral centres
achiral due to an internal plane of symmetry
this symmetry causes the compound to be superimposable on its mirror image

Question 2

define the term racemic mixture

Answer 2

1:1 mixture of 2 enantiomers of a chiral compound. The 2 enantiomers in a racemic mixture cancel each other’s optical activity, making the mixture optically inactive. it has equal amounts of 2 enantiomers.

Question 3

define hydrophobicity

Answer 3

The tendency of a substance to repel water or not dissolve in water. typically non polar. oil is an example

Question 4

define hydrophilicity

Answer 4

the tendency of a substance to interact with or dissolve in water. typically polar/ionic. salt is an example.

Question 5

explain the solubility of alkanes

Answer 5

they are non polar and do not dissolve in polar solvents like water. alkanes are soluble in nonpolar solvents like hexane or benzene. hexane is an example.

Question 6

why are low weight alchols soluble in water but higher weight alchols are not

Answer 6

Low-weight alcohols are soluble because they have small hydrophobic alkyl chains that do not interfere much with hydrogen bonding between the hydroxyl group and water.
high weight alcohols become insoluble becuase their large hydrophobic alkyl chains prevent efficient interaction with water, overpowering the hydrogen bonding ability of the hydrocyl group

Question 7

whats the strongest type of intermolecular force and why?

Answer 7

hydrogen bond is the strongest.
it involves a highly electronegative atom and a small, highly polarized hydrogen atom, creating a very strong and directional attraction between molecules.

Question 8

explain a condensation reaction and give an example

Answer 8

type of chemical reaction where 2 molecules combine to form a larger molecule, with the elimination of a smaller molecule.

Question 9

what is an intramolecular force

Answer 9

force that hold atoms together within a molecule. stronger than intermolecular.
ionic, metallic, covalant

Question 10

what is intermolecular forces

Answer 10

forces of attraction or repulsion between different molecules. these forces determine the physical propeties of a molecule
london dispersion forces, dipole-dipole interactions, hydrogens bonding

Question 11

what is covalent bonding

Answer 11

sharing of electrons between two non-metal atoms- water

Question 12

what is ionic bonding

Answer 12

the elctrostatic attraction between oppositely charged ions- sodium chloride

Question 13

what is london dispersion forces

Answer 13

temporary dipoles that occur due to the momentary distribution of electrons in molecules

Question 14

what is dipole-dipole interactions

Answer 14

attraction between -tive end of a polar molecule and +tive end of a seperate polar molecule

Question 15

what is hydrogen bonding

Answer 15

special type of dipole-dipole interaction where hydrogen is bonded to highly electro -tive atoms like fluorine/oxygen

Question 16

why is a kekule structure of benzene incorrect

Answer 16

because bonds of benzene are not fixed, benzene undergoes resonance. structure suggests that benzene has different lengths of bonds but they are all the same size

Question 17

what is zaitevs rule

Answer 17

during an elimination reaction, the more substituted akene will be the major product.

Question 18

define redox reaction

Answer 18

reactions in which oxidation and reduction of a compound or molecule take place.

Question 19

what makes a compound aromatic

Answer 19

must have planar/near planar structure
must have conjugated system of alternating single and double bonds
it follows huckels rule (4n+2pi)
it shows extra stability due to electron delocalization over the ring structure.

Question 20

define a chiral carbon

Answer 20

a carbon atom that is attached to 4 different groups, this gives the carbon a non-superimposable mirror image

Question 21

what are enantiomers

Answer 21

non-superimposable mirror images of each other. same molecular formula but differ in arrangemant of the atoms

Question 22

what is diastereomers

Answer 22

stereoisomers that are not mirror images of each other. same molecular formula but differ in arrangement of atoms and are not related by reflection. do not have identical physical properties

Question 23

define a nucleophile

Answer 23

a species that donates electrons to form a new chemical bond. it has a high electron density and seeks +tively charged/ electron-defient centers to react with. typically are anions.

Question 24

give an example of a nucleophile

Answer 24

hydroxide ion: it has a lone pair of electrons on the oxygen atom which it can donate to an electrophilic carbon

Question 25

define a leaving group

Answer 25

atom or group that departs from the molecule, taking electrons with it.

Question 26

give an example of a leaving group

Answer 26

chlorine: in the reaction of ethyl chloride undergoing nucleophilic substitution, the chlorine acts as the leaving group.

Question 27

how do the strengths of dipole-dipole forces compare with the strengths of typical covalent bonds

Answer 27

dipole-dipole is much weaker, dipole dipole are intermolecular forces covalant bonds are intrammolecular covalant bonds requires more energy

Question 28

what 4 types of electrophilic aromatic substituition (EAS) reactions do benzene and aromatic compounds undergo

Answer 28

Halogenation- addition of a halogen nitration-addition of a nitrate sulfonation-addition of a sulfonic acid group friedal crafts alkylation- addition of an alkyl group

Question 29

explain the regioselectivity of E1 reactions

Answer 29

E1 reactions are regioselective. major products formed will be the more stable and substituted product. only 3 degree haloalkenes undergo E1 reactions

Question 30

what makes a good leaving group

Answer 30

good leaving groups are weak bases. bad leaving groups are strong acids

Question 31

explain the difference between a nucleophile and a base in terms of substitution and elimination reactions

Answer 31

for a subsitution reaction a nucleophile will attack the partially +tive C atom that is directly bonded to the halogen atom in an elimination reaction a base will remove a proton from the B-carbon of a haloalkane

Question 32

Resonance theory

Answer 32

attempts to explain the structure of a chemical species, where single structure cannot adequetly represent it.

Question 33

resonance energy

Answer 33

difference in energy between a resonance stabilised hybrid and its lowest energy resonance form

Question 34

give two metal hydrides used as a reducing agent for carbonyl compound and briefly explain

Answer 34

soidum borohydride and lithium aluminium hydride serve as reducing agents. sodium borohydride is used for milder reductions lithium aluminium hydride is a stronger reducing agent and can reduce a wider variety of carbonly compounds

Question 35

what type of molecule are london dispersion forces the only major intermolecular forces?

Answer 35

present in all molecules but are the only major intermolecular force in nonpolar molecules

Question 36

are london dispersion forces relatively strong or weak?

Answer 36

relatively weak, strength increases with molecular shape and size

Question 37

explain the stability of carbocations with respect to the inductive effect

Answer 37

stability of carbocations increases as the number of alkyl groups increases. the +tively charged carbon polarizes electrons of adjacent sigma bonds towards it. the +tive charge on the cation is thus localized over the nearby atoms the larger volume over which the +tive charge is delocalized , the greater the stability of the cation. in other words the more atoms that share a charge the more stable the species becomes