Lecture 4

Question 1

what is acidity and basicity

Answer 1

acidity - The measure of the tendency of a compound to lose a proton.

basicity - the measure of a compound affinity for proton.

Question 2

the stronger the acid

Answer 2

the weaker its conjugate base is

Question 3

Equiblruims arrow length in acid-base reactions will favour the products if

Answer 3

the conjugated acid of the base that gains a proton is weaker than the acid that donates the protons in the first place

(it points towards the weaker acid)

Question 4

what are some organic acids/bases

Answer 4

Carboxylic acids, alcohols, and amines

Question 5

how can we assess the strength of a molecule’s basicity by protonation

Answer 5

using the rule that the stronger the acid the weaker the conjugate base we can measure the pKa of the protonated base and see if it’s acidic or not, the more acidic it is the weaker of a base the original molecule is.

note (the pronated molecule will act as an acid now because of the extra hydrogen)

Question 6

what are the relative pKa values of the organic compounds

Answer 6

pKa < 0 - Protonated alcohol. protonated carboxylic acid, pronated water

pKa ∼ 5 - carboxylic acids, protonated aniline

pKa ∼ 10 protonated amines, phenol

pKa ∼ 15 alcohol and water

Question 7

the value of the equilibrium constant can be calculated by

Answer 7

pKeq = pKa(reactant acid) - pKa(Product acid)

Question 8

the strength of an acid is determined by and why

Answer 8

the stability of its conjugate base, the more stable the base is the the stronger the acid and that is because the more stable the base is, the better it bears the electrons left by the hydrogen, this also means that it is a weak base which follows out rule (weak base —> strong acid)

Question 9

what are the two factors that affect the stability of a base

Answer 9

electronegativity (going across a period): when atoms have the same size the strongest acid is the one with the most electronegative atom holding the acidic hydrogen and that is because the more electronegative atom will bear the negative charge better.

Hybridization: since hybridization affects electronegativity and electronegativity affects the strength of an acid then the hybridization affects the strength of the acid where the sp is more electronegative than sp^2 which is more electronegative than sp^3 meaning an acidic hydrogen attached to a sp hybridized atom is more likely to be donated than a proton attached to a Sp^2 atom.

size (going down the group): when it comes to anions of different sizes the anion that has the biggest size is the one that is most stable and will form the strongest acid even if it is not the most electronegative

Question 10

why does the hybridization of the atom affect its electronegativity

Answer 10

electronegativity is the measure of teh ability of an atom to pull electrons closer to itself and generally, the average distance to the nucleus from an s orbital is shorter than the average distance to the nucleus in p orbitals, so teh sp hybridized is the most electronegative since it has the more S character.

It is important to note that the more the charge is brought closer to the nucleus the more stable the carbanion so the weaker of a base it is)

Question 11

why does size have a more significant effect on the stability than electronegativity

Answer 11

because with a bigger size, there is a larger volume for the negative charge to occupy which provides way more stability than electronegativity

Question 12

what is the inductive electron withdrawal

Answer 12

it is when the acidity of a compound increases as an electronegative atom is substituted onto a nearby atom, where the electronegative atom would withdraw electrons from the atom holding the acidic hydrogen making it more likely to be lost. This is further demonstrated by looking at the base that forms from the substituted compounds where we see that the negative charge formed on the atom holding the electron is taken away a bit by the electronegative atom making it stabilize the charge better so a more stable base = a stronger acid

Question 13

The inductive electron withdrawal increases as

Answer 13

the electronegativity of the atom attached increases and as the distance between the atom holding the acidic hydrogen and the substituted electronegative atom decreases

Question 14

why are carboxylic acids more acidic than alcohols

Answer 14

1. the inductive electron withdrawal is greater at the carboxylic acid since it has a hydrogen atom attached to the carbon pulling the negative share and stabilizing the compound
2. because once the compound is deprotonated the electrons left in the alcohol are localized while the electrons left in the carboxylic acid are delocalized between the carbon and two oxygen leaving a resonance structure that increases its stability so it will then form a stronger acid

Question 15

how can you determine which atom in the compound has a stronger basic atom when there are delocalized electrons

Answer 15

draw all the resonance structures then see which atoms are most electronegative.

In case both are electronegative check which has a larger negative charge.

Question 16

what does the Henderson-Hasselbach equation

Answer 16

a compound will exist in its acidic form if the solution it’s in is more acidic than its pKa and a compound will exist in its basic form if it is in a solution more basic than its pKa

if pH < pKa then acidic

if pH > pKa then basic

Question 17

non-polar compounds are more soluble in

Answer 17

non-polar solvents

Question 18

how can the Henderson-Hasselbach equation help with separate mixtures

Answer 18

by relating the pKa of the solute with the pH of the solvent and vice-versa, for example, diethyl ether and water don’t dissolve in each and they form two layers, so given a mixture of an amine and a carboxylic acid where the pH of the water layer formed from the diethyl ether and water solution is less than the pKa of both the carboxylic acid and the amine, we can see using the Henderson-Hasselbach equation that the carboxylic acid will exist in its acidic state (which is non-polar making it dissolve in the diethyl ether solution) and the amine will exist in its acidic state ( which is protonated so its polar so it dissolves in water) therefore we have separated the mixture

Question 19

what is the general molecular formula of cyclic alkene and alkane

Answer 19

alkene - CnC2n-2

alkane - CnC2n

Question 20

what is the degree of unsaturation

Answer 20

It is the total number of Pi bonds and rings in a compound.

For example: alkene and cyclic alkanes ae unsaturated while alkanes are saturated

Question 21

when we have a functional group and a substituent in a compound which would take priority in naming

Answer 21

the functional group

Note the functional group also included the double bonds

Question 22

what are Vinylic carbons, allylic carbons, vinylic hydrogen, and allylic hydrogens

Answer 22

Vinylic carbons - the sp^2 carbons of an alkene

Allylic carbons - the carbons adjacent to the vinylic carbon

Vinylic hydrogen - hydrogen attached to a vinylic carbon

Allylic hydrogen - hydrogen attached to an allylic carbon

Question 23

what is an allyl group and a vinyl group

Answer 23

Allyl group - it is the smallest group with an allylic carbon on it

Vinyl group - it is the smallest group with an vinylic carbon on it

Question 24

for maximum P-P parallel overlap in alkenes, we need

Answer 24

we need both P orbitals to be parallel and that occurs when they all of the 6 atoms in the double bond system is in one plane (y3ani 120 degree bond)

Question 25

what is the simple rule that explains why certain groups react in a certain way

Answer 25

an electron-deficient species is attracted to an electron-rich species

Question 26

what is an electrophile

Answer 26

it is an electron-deficient species and can be determined by a positive charge, a partial positive charge, or a compound with an incomplete octet.

Question 27

what is a nucleophile

Answer 27

an electron-rich species that has a lone pair of electrons to share and they can be determined by a negative charge, a partial negative charge, a lone pair of electrons, or by a double/triple bond

Question 28

what can we call Lewis acids and bases

Answer 28

lewis acids are electrophiles and Lewis bases are nucleophiles so a reaction between an electrophile and a nucleophile can be described by a lewis base and lewis acid reaction.

Question 29

what is the mechanism of the reaction

Answer 29

it is the step-by-step description of the process by which the reactants are changed to products

Question 30

what is the mechanism of HX with alkenes

Answer 30

we can see that the electron cloud present in the alkene double bond is very dense meaning that it is a nucleophile so when it comes to contact with a hydrogen halide it is attracted to the partial positive charge of the hydrogen which acts as an electrophile. The Pi bond in the alkene double bond breaks and forms a bond with the hydrogen in the hydrogen halide but in order for that bond to be made the electrons shared by the hydrogen and the halide are taken by the halide giving it a negative charge and forming a carbocation in the alkene as the electrons in the pi bond are used to form a sigma bond with hydrogen leaving the other carbon electron-deficient which then causes the nucleophile of the bromide to react with the carbocation electrophile forming an halogenoalkane. Note that the pi bond is broken because the sigma bond is stronger Look at the full mechanism in the book page 199

Question 31

the mechanism of alkene plus HX is called

Answer 31

electrophilic addition reaction (since we add the Electrophile of hydrogen)

Question 32

what is an energy coordinate diagram

Answer 32

it is a diagram that shows the energy changes that take place during a mechanism, where the total energy of the species is plotted against the progress of the reaction

Question 33

what is the transition state

Answer 33

it is when the reaction passes through its maximum energy state, where the structure of the compound is at the point in between the reactant and products where bonds would be partially broken and partially formed.

Question 34

what does the height of the transition state tell us

Answer 34

it tells us how much energy is needed for the reaction to occur, if its height is too large then the likeliness of the reaction occurring is very little.

Question 35

What is the general molecular formula for acyclic and cyclic Alkynes

Answer 35

acyclic - C2nH2n-2 Cyclic C2nH2n-4

Question 36

what is a terminal alkyne and an internal alkynes

Answer 36

a terminal alkyne is when the triple bond is on the end of the hydrocarbon chain and internal alkyne is when the triple bond is anyway but at the end of the chain

Question 37

what is the nomenclature name of alkyne.

Answer 37

substituted acetylenes (that how their common names are not systemic)

Question 38

how do we name compounds with two functional groups

Answer 38

1. number the carbon chains from the lowest caton chain being on the functional group with the greatest property 2. number the chain to make sure it has all the functional groups even if the base chain made isn't the longest chain the compound 3. in the case of double bond and triple bonds number the chain where the lowest possible values are numbered on the carbons attached to the double bond and triple bond, if there is a tie in the numbering where the lowest values would be the same the double bond will take priority and will have the lowest possible value 4. if more than one triple bond then diyne 5. always place the double bond in front of the triple bond when naming

Question 39

what are the priorities of functional groups

Answer 39

C=O > OH > NH2 > C=C = C≡C

Question 40

which is more stable internal alkynes or terminal alkynes

Answer 40

since alkyl groups are known to stabilize molecules such as alkene and carbocations they will also stabilize alkynes with internal alkynes being surrounded with more alkyl groups making it more stable.

Question 41

what are the physical properties of alkanes, alkenes, and alkynes

Answer 41

1. their bp increases as the molecular weight increases 2. they are insoluble in water but soluble in non-polar solvents 3. they are less dense than water

Question 42

why do alkynes have a higher boiling point and stronger London forces than alkenes

Answer 42

because alkynes are more linear than alkenes and the triple bond is more polarizable than the double bond, Therefore an alkyne has a larger bp compared with an alkene of the same carbon number. (also side note alkynes also have slightly larger bp values compared to alkanes while alkenes don't)

Question 44

why is phenol a weaker acid than carboxylic acid.

Answer 44

1. the inductive electron withdrawal by the carbon in the phenolate ion is not as great as the effect caused by the oxygen in teh carboxylate ion 2. the increased delocalization energy when a proton is lost is not as great in phenolate ion compared with the carboxylate ion and that is because the carboxylate ion forms two resonance contributors that are identical