lecture 4 Flashcards
is C more stable in the singlet or triplet state and why
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)
why are C=C bonds planar
they form strong multiple bonds
fragments have triplet ground states or small singlet-triplet energies.
which state does Sn like and why
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.
what is interelectron repulsion
when e- repel eachother in the same orbital // others
and the inert pair effect
if a singlet is preferred,, will the delta E s->t be positive or negative
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.
what is a genuine triple bond made up of
1 sigma bond
2 pi bonds that are degenerate
do lots of compounds have the ability to have a genuine triple bond
nope!! only a few classes of compounds can acc form a genuine triple bond
what classes of compounds can form genuine triple bonds
compounds with a valence 2p orbital
where orbital overlap is efficient
name things triple bonds are seen between
alkynes
cyanide
di nitrogen
nitronium cation
alkyne
c triple c
cyanide
c triple N-
- charge on N
di nitrogen
N triple N
nitronium cation
N triple O +
what structure do heavier elements have when they form triple bonds
heavier atoms with multiple bonds,, aka double or triple bonds,, will adapt a trans bent structure
are heavy main group compounds more likely to form double or triple bonds
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
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
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.
what is used to keep electrophiles away from multiple bonds aka double or triple bonds
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
why are there fewer compounds with a potential triple bond than a double bond
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
as seen in double bonded compounds: describe the availability of s electrons down a group
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
as seen in double bonded compounds: describe a trans bent structure
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
as seen in double bonds: do we need to sterically protect triple bonds
yessss with a bulky base
to prevent electrophilic addition to the triple bond
how would we draw a rlly scientific and really cool triple bond
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
