quiz material Flashcards
what is a feature of carbenes
neutral, regiospecific
what do carbenes make
cyclopropane
through what does the Simmons smith reaction form a cyclopropane
it will form a carbenoid which acts like a carbene
what is a radical
any atom with an unpaired electron
to make a radical, what do you need to do?
you need to put in energy, radicals are high in energy and are unstable
what are the three steps involving radical reactions
initiation, propagation, termination
what are the three ways to make a radical, what is this step called?
1) Halogen (Cl2,Br2) with heat or light
2) Organic peroxide (ROOR) with heat or light
3) AIBN Azoisobutyronitrile
this is an initiation step
why is H2O2 in a dark bottle
itll break down into radicals, a similar process occurs with ROOR
how do we characterize the bond between Cl-Cl and RO-OR
weak bonds, when subjected to light they homolytically cleave to form radicals
what forms when we react ROOR in light?
it forms two alkoxy radicals
why do we like to use AIBN to form radicals?
ROOR is toxic, Cl2 is a gas, Br2 is a liquid and are hard to work with
what is AIBN
it is a radical initiator that is solid and easy to work with
why do we like to use AIBN
it forms 2 radicals and N2 bubbles off in solution, this pushes the reaction towards products since its continously losing nitrogen gas
what is the intitiation step
it is the formation of a radical through the use of heat or light
what is a radical halogenation
A halogen atom replaces one or more of the hydrogen atoms of the alkane, and the corresponding hydrogen halide is formed as a by-product
what is a propagation step
it describes the chain reaction of radical formation. Where the presence of one radical reacts with other stable molecules to form more free radicals
what is the first step in radical hydrogenation of Cl2 and methane?
initiation, the Cl-Cl will homolytically cleave in the presence of light or heat
what is the second step in radical hydrogenation
the radical Cl reacts with the methyl to create an HCl byproduct and a methyl radical
what is the second part of the propagation step of radical hydrogenation of Cl2 and methane?
the radical methyl will react with a new Cl-Cl molecule and form methyl chloride and a new Cl radical (propagation step, it can be reused)
when does propagation stop?
when we stop supplying the reaction with starting material
what is the termination step
it is when we stop supplying the reaction with starting materials, any radical byproducts can now collide and form bonds together to create unfavorable products
what is a termination step
The termination steps actually reduce the number of radicals by consuming radicals, but not producing any.
if you have a reaction that only forms radicals, what step is it?
it is a initiation step
if you have a reaction that forms products AND radicals, what step is it?
it is a propagations step
if you have a radical reaction that forms no new radicals, what step is it?
it is a termination step
what is a disadvantage of radical halogenation with CH3 with Cl2
we keep removing halogens until we reach a fully replaced carbon tetrachloride molecule
it creates a mixture of products 1,2,3
what is an advantage of radical halogenation
it increases the functionality by transforming a unreactive alkane to a reactive alkyl halide
what is the order of stability for radicals?
3°>2°>1° due to the inductive effect
why is the benzyllic radical stable
it is stabilized by resonance
