lecture 4

Question 1

is C more stable in the singlet or triplet state and why

Answer 1

triplet fragment
(energy change from going to singlet to triplet is negative : exothermic)

energy to pair electrons up in the same orbital is higher than the energy needed to promote the e- to a higher energy p orbital (higher bc not hybrid and no s character)

Question 2

why are C=C bonds planar

Answer 2

they form strong multiple bonds

fragments have triplet ground states or small singlet-triplet energies.

Question 3

which state does Sn like and why

Answer 3

Sn likes being in the singlet state,, where e- is paired in the hybrid orbital (meaning energy needed to go from S -> T is positive,, bc its unflavoured and will require energy to do so)

energy required to pair e- in the same orbital is lower than the energy needed to promote the e- to the p orbital

bc the energ ygap between sp2 and p is larger! and due to interelectron repulsion.

Question 4

what is interelectron repulsion

Answer 4

when e- repel eachother in the same orbital // others

and the inert pair effect

Question 5

if a singlet is preferred,, will the delta E s->t be positive or negative

Answer 5

it would be positive bc ur changing from smt the compound likes and is stable in,, to smt it doesnt like and smt its not stable with.

Question 6

what is a genuine triple bond made up of

Answer 6

1 sigma bond
2 pi bonds that are degenerate

Question 7

do lots of compounds have the ability to have a genuine triple bond

Answer 7

nope!! only a few classes of compounds can acc form a genuine triple bond

Question 8

what classes of compounds can form genuine triple bonds

Answer 8

compounds with a valence 2p orbital

where orbital overlap is efficient

Question 9

name things triple bonds are seen between

Answer 9

alkynes
cyanide
di nitrogen
nitronium cation

Question 10

alkyne

Answer 10

c triple c

Question 11

cyanide

Answer 11

c triple N-

• charge on N

Question 12

di nitrogen

Answer 12

N triple N

Question 13

nitronium cation

Answer 13

N triple O +

Question 14

what structure do heavier elements have when they form triple bonds

Answer 14

heavier atoms with multiple bonds,, aka double or triple bonds,, will adapt a trans bent structure

Question 15

are heavy main group compounds more likely to form double or triple bonds

Answer 15

theyre more likely to form triple bonds

however forming a triple bond using 3 orbitals means theres only one orbital for a substituent or a lone pair

Question 16

bc heavy main group elements that form triple bonds only have 1 orbital to either bond to a substituent or a lone pair what does this mean

Answer 16

steric protection of the triple bond usually requires an exceptionally bulky ligand.

to prevent it from attacking other things due to the bulky groups repelling any possible electrophiles.

Question 17

what is used to keep electrophiles away from multiple bonds aka double or triple bonds

Answer 17

bulky groups are used as a double// triple bond restricts thr amount of substituents bonded to it. which means the multiple bond isnt sterically protected as theres nothing protecting it.

so we use a bulky base as a substituent as this will sterically hinder electrophiles from attacking the multiple bond

Question 18

why are there fewer compounds with a potential triple bond than a double bond

Answer 18

when we have a triple bond,, theres only one orbital left to bond to a substituent

when we have a triple bond we use an s electrons: sp

Question 19

as seen in double bonded compounds: describe the availability of s electrons down a group

Answer 19

down a group,, s electrons are less available for bonding due to the inert pair effect: due to their shielding and penetrative properties: also the larger energy difference between s and p orbitals the lower u go. prevents s from being used. can lead to lower than expected OS due to p e- being used instead

s electrons penetrate closer to nuc: more stable,, less chemically reactive

Question 20

as seen in double bonded compounds: describe a trans bent structure

Answer 20

double bond with the left r groups pointed down and the right handed r groups pointed up.

each sidde has a dashed and a wedged side.

the bond strength between the main group elements is reduced

Question 21

as seen in double bonds: do we need to sterically protect triple bonds

Answer 21

yessss with a bulky base

to prevent electrophilic addition to the triple bond

Question 22

how would we draw a rlly scientific and really cool triple bond

Answer 22

two circles to be the main group element

they each have 1 e- which are opposite spins

then theres an e- pair in one of the hybrid orbitals of each main group element and theres an arrow from this to an empty hybrid orbital.

so its like a dative type bond between the 2 main group elements.

and theres a sigma bond between them

Question 23

inorganic rings can be either

Answer 23

homocyclic
heterocyclic

Question 24

homocyclic inorganic ring

Answer 24

only one element is used

Question 25

heterocyclic inorganic ring

Answer 25

more than element is used two or more elements are used

Question 26

every inorganic non metal has what

Answer 26

they have a homocyclic ring

Question 27

C-C is a really strong bond which meansss

Answer 27

they have extensive ring chemistry cyclic alkanes and aromatics

Question 28

what is boron the only one known to form

Answer 28

boron is the only main group element known to form an extensive pi delocalised homocyclic rings and cages (boron hydrides)

Question 29

some E-E bonds are strong but their XXX are stronger leading to XXXX

Answer 29

some E-E bonds are strong but their E-X bonds are much stronger (ionic contribution) this leads to instability with respect to hydrolysis, hydrogenation or halogenation

Question 30

Group 3 and 5 elements like to bond with which element

Answer 30

they like to bond with OXYGEN,, over itseld, H or Cl due to O being so electronegative,, it gives ionic contributions due to the electronegative differences.

Question 31

recall the pi delocalised heterocycles containing N

Answer 31

Borazines Cyclophosphazenes Cyclothiazenes

Question 32

describe borazines

Answer 32

6 membered BN ring B bonded to H N bonded to H conjugated double bonds

Question 33

describe cyclophosphazenes

Answer 33

6 membered PN ring P bonded to 2 Cl N not bonded to anything conjugated double bonds

Question 34

describe cyclothiazenes

Answer 34

6 membered N S ring S bonded to Cl N bonded to nothing conjugated double bonds

Question 35

when u see pi delocalised heterocycles what should u think

Answer 35

cyclic ring made up of 2 or more different elements conjugated double bonds

Question 36

what are the 2 synthetic methods for making inorganic rings

Answer 36

condensation azide route

Question 37

how is condensation used to make inorganic rings

Answer 37

driven by entropy loss of HCl or H2 (from the N-H and E-Cl) elevated temps are required (120-150) to drive off the HCl formed. a base can be added to prevent HCl being formed as it is dangerous

Question 38

which base can be added to condensation to prevent HCl being formed when inorganic rings are being synthesised

Answer 38

pyridine (6 ring with N) or Nh3

Question 39

driving force for condensation reactions when making inorganic rings is

Answer 39

entropy bc TS bc gas is being made

Question 40

when making inorganic rings via condensation,, what do we do when using milder conditions

Answer 40

we use an alkali metal salt or a trimethysilyl derivative the salt formation is the driving force of the reaction : thermodynamically driven NaCl LiCl

Question 41

what is the other,, less popular route for making inorganic rings

Answer 41

thr azide routeeee

Question 42

why is the azide route less favoured

Answer 42

bc azides are explosiveeee esp if large quantities of inorganic rings are needed

Question 43

what is used to make main group azides at a low tempppp

Answer 43

mild condensation reactions using LiN3 NaN3 Me3SiN3 low temp warming these releases N2 to generate reactive monomers which oligomerise decomposition of the azide depends on the substituents

Question 44

what is an oligomer

Answer 44

a polymer made up of only a couple of repeating units its phycial properties are dependant on chain length

Question 45

Borazanes: what are they

Answer 45

aliphatic BN bondssssss

Question 46

borazine BN is isoelectronic with what

Answer 46

C2 that means BN can be used to replace CC bonds

Question 47

Alkyne andddd BN form

Answer 47

Borazyne B triple N

Question 48

alkene and BN

Answer 48

borazene B=N

Question 49

alkane and BN

Answer 49

borazane B-N

Question 50

describe amine-borane adducts and how theyre made

Answer 50

N dative bond to B using lone pair H3N-->BH3 or R groups theyre colourless low mp crystalline solids isoelectronic with alkanes donor acceptor adducts

Question 51

whats an adduct again

Answer 51

when 2 molecules react and bond together and the product has all the atoms of the separate molecules

Question 52

lewis structure of an amine-borane adduct

Answer 52

R3N+ ---> BR3 - bc N donates its lone [air to B meaning its more positive relative to before,, when it still had its lone pair and was neutral

Question 53

partial charges structure of amine-borane

Answer 53

R3N - --- BR3 + but partial charges bc N is more electronegative than B

Question 54

Borazines

Answer 54

cyclic!!!! borazine = limozene = car = cyclic bc wheels. inorganic benzene BN cycle with H on each thing B3H3N3 conjugation swell.

Question 55

whats an azide

Answer 55

and azide is used in the azide synthesis route to make inorganic, pi delocalised heterocyclic rings. N=N=N middle N is (+) N thats on the end is (-)