6d Flashcards
describe a cyclobutadiene
butane but with double bonds and cyclic
what is the huckels rule for
- to see if smt is aromatic
- 4n+2
is the amount of pi electrons it needs
should be an integer
how many pi electrons does butadiene have
butane with 2 double bonds
so 4 pi electrons
doesnt fit huckels rule do cyclobutadiene and butaniene are not aromatic!!!
bonds lengths of butaniene and cyclobutandiene due to it not being aromatic
it doesnt have identical bond lengths!!
so cyclobutaiene isnt a square but more of a rectangle shape,, theres distortion
describe the MO of the pi system of cyclobutadiene and explain why the bonds arent all the same length
u always start with the fully bonding one where all the p orbitals are in phase. this mo is fully bonding and most stable
then u have 2 mo’s, which both have one node and these are nonbonding bc the inphase and out of phase interactions cancel out!
then u have the full antibonding one where u have 2 nodes.
the bond lengths arent the same bc the nonbonding orbitals become either bonding or nonbonding bc distortion occurs bc they arent filled equally. distortion removed degeneracy.
increasing the bond length reduces either the antibonding or bonding interaction depending on where the node is,, allowing the other interaction to be more prevalent.
the fully bonding mo of cyclobutadiene overlaps with what d orbital
the dz^2 one !!
the 2nd energy mo of cyclobutadiene interacts with what d orbital..
look at the bottom of the p orbitals and see if theyre filled or not and then make a d orbital that fits to this.. its normaly the dzy and this is where pi donation occurs
this one has more bonding character after distoriton occurs
whats the 3rd mo of energy in cyclobutadiene
its the dzx
with the distortion causes the antibonidng nteraction to be strenghtened.
whats the highest energy mo of cycobutadiene interacting with what d orbital
the dxy this is where delat backbonding occurs!!!
when is distortion favoured and what electron count do these molecules usually have
favoured for ANTIAROMATICS AKA COMPOUNDS WHERE THE E- COUNT DOESNT RESPECT HUCKELS RULE
DISTORTION IS FAVOURED
WHEN IS THE PROPER STRUCTURE WITH NO DISTORTION FAVOURED
when they respect huckels rule!!!!!! when theres no distortion bc the orbitals are filled equally.
describe the order in which d orbitals overlap for backbonding
dz^2 : sigma bonation
dyz : pi donation
dzx : pi backbonding
dyx : delta backbonding
all known complexes of butadiene have what ring structure
they all have a C4 square ring
what do we treat cyclobutadiene as
a neutral 4 e- donor
how can we synth complexes with cyclobutadiene
cyclobutane with a double bond on one side and 2Cl’2 on the other + Fe(CO)9 —> cyclobutadiene structure eith Fe in the middle and the (CO)3 at the bottom : ferrocene looking molecule + FeCl2 + 6CO
second way of synthesising complexes with cyclobutadiene:
u have Cl- Co - PPh3 bonded to 2 alkynes with ph on each end
whats cyclooctatetraene,, descibr it and what is the small name for it
its called COT
its cyclooctane aka an octane but in a circle with 4 conjugated double bonds
is cyclooctatetraene aromatic
it has 4 double bonds meaning it has 8 pi e-.
4n+2 = 8
nope
its antiaromatic meaning its onlyt aromatic and all bonds will be the same length once u coordinate it,, bc then it gets 2e- from the metal.
u have the bonding and antibonding and then the other ones are paired up with nodes between them
cyclobutadiene is a long.n type of ligands,, what number tho
long.n 4
bc the 4 carbons are not independent
cyclooctatetraene is what type of long.n ligands
a long.n 8 ligand
bc the 8 carbonds are not independent
what do we treat cyclooctatetraene ligand as
a 10e- C8R8 ^-2 donor ligand
whats wrong with the cyclooctatetraene ligand tho
its hella big when planar
meaning it only coordiantes with metals in the f row!!!
aka the actinides
what metals can COT aka cyclooctatetraene complex with
we see it complex with uranium!!!
u have COT - U - COT
aka bis(COT)U
whats the electron count of bis(COT) U
COT - U - COT
COT = C8H8 ^-2 (10e-)
U = 4+ (2e-)
COT = C8H8 ^-2 (10e-)
u have 22e- in total !!!
18e- rule isnt applied to this complex bc its not using a d block metal,, but an f block metal.
when u have COT,, its obvs a long.n 8 ligand but what else can it be and how can we do it
it can be a long.n 4 and long.n 2 ligand
this is done by only using some double bonds to coordinate with the metal.
when double boonds arent in conjugation and are bonded to the same metal,, they count as separate bc theyre not in conjugation.
so when its bent like a taco holder with the double bonds at the top and at the bottom its a 4 x 2e- donor bc all the double bonds are independednt
when its just kinda bent /// slanted like a stair in the staircase its a 2 x 4e- ligand bc the pair of double bonds coordinated to the same ligand are in conjugation.
when do we distort energy levels
when energy levels arent equally populated // when orbitals arent equally populated
benzene has how many pi electrons
6e-
is benzen aromatic or antiaromatic
what will happen if it was benzene 2+
benzene is aromatic bc it fits huckels rule
if it was antiaromatic it would be benzene2+ bc that would mean u have 4e- and that doesnt fit huckels rule.
bc its aromatic,, the orbitals are filled equally so theres no need for distortio n
describe the mo diagrams of benzene and the order of d orbitals and interactions between them.
fully bonding one = dz^2 = sigma donation
bonding 1 node : dyz, dzx : pi donation to each depending on orbital symmetry and where the node is
2 antibonding ones : 2 nodes : dxy and dx2-y2 = delta backbonding
fully antibonding = no d block metal has an orbital whos symmetry matches it and can lead to an interaction
in benzene,, does the sigma interaction or pi interaction larger
the pi interaction is larger bc theres 2 mo’s that mave pi interaction (the bonding ones with one node)
compared to the one sigma donation (the fully bonding one with no nodes)
benzene is a what long.n ligand
its an n.long 6
bc all the carbons are not independednt from one another. they work as a group.
so what 3 interactions does benzene as a ligand have with its metal
sigma donation
pi donation
delta backbonding
and these all give the same amount of e- : aka take // give 2e- to bonding and antibonding orbitals.
so all c-c bonds are equal in legnth
why are the cc bonds in benzene equal in length
bc sigma bonding // pi bonding and delta backbonding occur in a way that keeps all the orbitals degenerate in terms of how many e- are in each of them - allowing degenerate orbitals to have the same amount of e- so theres no need for distortion!!
a long.n 6 arene ligand maintains what
it maintains equal CC bonds
is benzene a good ligand
yess!! benzene is a good ligand
describe a ligand with benzene in it and how to make it
benzene - Cr - benzene
6e- + 6e- + 6e- = 18e-
Cr gas + 2C6H6
sandwich structure
its a very stable compound
how can benzene be added to a metal for it to form a complex and be a ligand
Cr(CO)6 + benzene - OMe
3(CO)Cr - benzene - OMe
still 18 e- (CO give 2e- each)
a CO ligand gives how many e-
gives 2e-
whats an arene
an aromatic hydrocarbon
can u have long.n4 and long.n 2 arenes // benzene
yes!! just depends on how many Carbonds and double bonds u want to use to bond to ur metal .
1 double bond = long.n 2 bc ur using 2 C to become besties
using 2 double bonds that are conjugated together = long.u 4 bc ur using 4 carbons to be besties and coordinate to the metal
