Practice English Speaking&Listening with: Question 3 Radical and Organometallic Line Reactions

Alright let's look at some more line reactions in number three our first up

is radical halogenation of cyclopentane because of its rotational symmetry about

an axis here that's coming out of the page at us going back in like a wheel

spoke there we can rotate any one of these corners to the same position

relative to one another and get the same structure back to our to our eye so that

makes all of those positions equivalent and we make a single product with no

chiral center of a chlorine at any one of these five positions we could draw it

any way you could have drawn it like this you could have also drawn it with

perspective like this but there is no enantiomer because this is not a chiral

compound there's a plane of symmetry that cuts this molecule in half making

these groups the same on both sides got to have four different groups to make

something chiral right so most likely most people here wrote just the single

bond here to chlorine for halogenation if you did put both you've got a

one-point deduction if you indicated that there were two products here

alright so our next reaction we want to make an organolithium and from an alkane

so we don't have any reaction that takes us directly from an organolithium or

from an alkane to an organolithium x' but and we do have a single reaction for

alkanes that would highlight this tertiary position and that would be to

brominate with a photon here of UV light okay or a photon irradiation well that

gets a bromine to that position and so step one here gets us to here and then

we can add the lithium in step two by just writing lithium lithium solid you

could have left it like this so you can also

written hexanes if you wanted to indicate the solvent one point per line

and again anything missing from line number one it gets a point off

anything missing from line number two gets a point off forgetting to divide it

up into two steps gets one point off if everything else is correct all right

looking at our next one here we are making a gilman reagent we've got the

proper stoichiometric ratios for this we didn't have to have those if you were

providing them to us we didn't need this in any other place on the exam that's

okay we went ahead and put it in there that we needed an excess of lithium and

so the first thing that you would do that step one would convert these alkyl

halide equivalents into an alkyl lithium and then from there into our gilman

reagent so a couple ways to draw this we've got four carbons and so we need to

make sure that those four carbons one two three four in the parentheses

there's two equivalents and then copper lithium makes up our gilman that's two

points now you can also have written this out as a line structure

copper lithium there so CH3 and then 3 CH2s with subscript 2 for the entire

group copper lithium to get that as well so either way is fine if I can draw a

U there Cu and then Li to make that gilman reagent for two points

looking at our next reaction we have a primary halide at the less substituted

position of an alkene that's anti markovnikov halogenation so we need HBr

and peroxide one point each for Hbr and peroxide directly from an alkene looking

at our next one we have a primary halide which we are allowed to couple gilman

reagents to and so the methyl group of that gilman is going to replace the

bromine and we end up with isopentane as our product here two points

finally Grubbs catalyst we've got two alkenes that are in the same molecule so

this is ring closing metathesis and with ring closing metathesis we are going to

cut both of these in half the CH2 ends are going to come together and bubble

away as ethylene gas so you could have put that in the box not needed here we

only needed the final product so the left hand side of the molecule is not

affected the benzene ring double bonds are stable they are not reactive like

normal alkenes and the alkene side

creates a five membered ring with that double bond as these two ends 1 2 3 4 &

5 come together in the final product so 2 points all or nothing for that box