amaroso practice questions Flashcards
A new zintyl phase was prepared by the reduction of tin with sodium in liquid
ammonia.
The compound was found to have an elemental composition of:
% Sn, 92.07; %Na, 7.93.
Mass spectrometry indicated that the anionic cluster has an average mass of 1068.3 a.m.u.
Give the structure of the anionic cluster. [8]
- zintyl means cations and anions
- so think of what is ur cation and what is ur anion
- using the one with most info ,, try find how many of them are there
- and then u need to find its charge,, and to find its charge u need to find out how many of the other one there is.
- do think by working out how much 100% weighs
- once u have the number of the species and the charge,, u can apply wades rules to it.
- Sn is normally sp hybridised so 1 e- in the p orbitals and then an electron pair in an sp orbital,, meanign it gives 2e- for cluster bonding.
how do u figure out how many electrons smt has for cluster bonding,, use BH and CH as examples
BH = 3 valence electrons, but u use one of them to bond to the H,, so u have 3-1 so u have 2e- for cluster bonding.
CH = C has 4 valence electrons,, it uses one of them to bond with H,, so 4-1 = 3 ,, so CH gives u 3 electrons for cluster bonding.
are Boron Boron or Boron Carbon bridges preferred
boron boron bridges are preferred!!!
over than BC,, so if u need to add more hydrogens,, they do to the BB sides
what do we never see bridging between
we never see bridging between Carbon Carbon!!! unless we have to
when we want to see how many isomers there are of something,, what can we do to see,,, aka for the pentagonal bipyramid structure,, how many different isomers can there be if we have C2B4H8
if we have all those atoms we have 3 different isomers!!!
we can have a C at the 1 and then the 2 position.
we can have a C at the 2 and 3 position
we can have a C at the 2 and 4 position.
the last two are different bc tu have a CC bond in one but not in the other.
aka to see if things are different isomers,, u can look at if they have the same number of identical bonds,
when we’re asked to do the Boron nmr and we have 3 different boron environments,,, what do we need o do
we just need to be careful and make sure we acc figure out how many B environments there are.
bc we dont need to split the B’s with the B’s.
so if u just have 1 boron environment u get 1 singlet.
if u have 2 boron environments u get 2 singlets
if u have 3 boron environments u get 3 singlets
we dont need to do Boron Boron coupling,, bc its too complex
when we figure out the wade structure of a complex,, and we want to figure out how many peaks we get,,what do we ignore
we ignore Boron Boron coupling,, its too complex so we just say theyre singlets
when u have a 13C at the apex and a 13C at the bottom shape,, do these split a B// another atom by different amounts
yesss
they split the B by different amounts
so if a B is 1J bonded to 2 x 13C,, one in the apex and one in the bottom shape,, what will we see in B spec
u will see a doublet of doublets!! bc the first 13C splits it into a doublet and then the second 13C also splits the doublet into a doublet,, so u get a doublet of doublets
somthing being isolobal means what
it means their frontier orbitals have similar energy and therefore similar symmetry.
theyre also isoelectronic meaning the same number of valence electrons
when we have a metal carbonate as one of out compounds for a structure,, how do we figure out how many e- it donates for cluster bonding
CO gives 2 electrons,, and normally its (CO)3 so u do 2x3 = 6
and then u do the metal d electron count - 6
to figure out how many u have for cluster bonding
whats a zintyl compound thingy
an Sn and a p block element
when doing wades rules what do u need to rmemeber
after u divide by 2 u need to -1!!!!!
when u have a tricapped trigonal prism,, and 1 have 1 random atom, how many isomers can u make
u can have 2 diff isomers,, either with the random atomas a cap or the random atom as part of a prism.
boranes are made up of BH units,, describe the hybridisation of boranes
B is sp3 hybridised!!
meaning it has 2 sp orbitals,, remmeber the diff phasing for each bit of the orbital
and then it has 2 p orbitals
BH,, B is obvs sp and the small bit of the sp orbital is in phase with the H, the larger sp orbital bit we label as radial,, the 2 P orbitals we label as transgential
when ur doing the molecular formula from the analysis thing,,, when it doesnt add up to 0 what do u need to do
the part that missing goes to oxygen!!1
in the molecular analysis thing,, when u have Fe and C and O,, what do we nroamlly say it is
we says its Fe(CO)3
up to now whenever theres been like 4.38 H’s we count it as how many
weve been rounding up no matter what
how do we know PH gives 4 e- in the fragment.
we see P is in group 5, then it uses 1 to bond to H so u have 5-1 = 4.
Explain what the Schlenk equilibrium for Mg alkyl species is and how it
can be confirmed
2MgRX <—> MgR2 + MgX2
u can use Mg NMR to confirm each species,,
theres an equilibrioum so taking the NMR we can see what theres more of using the peak chem shift.
u normally get an Mg-R-Mg bridge and u can get ligand exchange due to this
Mg-R-Mg bridge is usually 3c-2e,, like Al2Me6 or B2H6,, bc Mg is in group 2, meaning its e- deficinet unlike group 5
Give the structure of tBuLi in hexane solution and explain how
spectroscopic methods can be used to confirm it.
draw it out if u cant figure out what they want. Li-C - (CH3)3
draw out the tetrameric structure
u can use Li NMR with 13C doped carbons whih will show that Li is bonded to 3 C!!
or u can use 13C nmr with 6Li to show u C is bonded to 3 Li.
Explain how the products from the reaction of an amine with diborane may
be spectroscopically investigated. What products are typically formed
- homoleptic
- heteroleptic cleavage
- 11B[H] NMR can be used to to identify the different products due to as one will only give a singlet as its only bonded to 4 H’s. which dont split the peak due to it being hydrogen decoupled.
Explain the bonding in borazine and with reference to its reaction with a
nucleophile (e.g. Cl- in HCl) comment on the aromaticity of borazine
Show how sp2 hybridisation of B and N leads to benzene like structure ( 1
mark). Show how lone pair of N donates to empty p on B ( 1 mark).
Formally written as B-— N+ but actually B+— N- (1 mark). Cl- adds to
B not N. Reaction is addition not substitution. Does not try to retain
unsaturated nature. Not aromatic (up to 2 marks).
Methyl aluminium gives an 1H NMR spectrum consisting of two peaks
when collected at -150˚C and one peak at 20˚C. Explain these
observations
Draw out dimeric structure (2 marks). Show there are 2 H environments.
(1 mark). Discuss fluxional behaviour (up to 2 marks)
Explain why R2C=CR2 is a planar molecule, but R2Sn=SnR2 is not
Discuss non-classical double bond. Consider energy difference between s
and p orbitals. Show s to p bonding in Sn and sp2 hybridisation in C. up to
5 marks.
