Hey men I'm having actually trouble knowledge the distinctive signals on a couple of molecules.

You are watching: Cis-1,2-dimethylcyclopropane

For trans-1,2-dimethylcyclopropane, the price in my book says it has actually 3 signals.

For cis-1,2-dimethylcyclopropane it has actually 4 signals with the H's top top C3 gift counted together two different signals which I would I guess is due to the fact that they space diastereotopic hydrogens.

Why wouldn't the H's ~ above C3 because that trans-1,2-dimethylcyclopropane likewise be diastereotopic though, making the compound 4 signals?

Or rather...how room the H's top top C3 that cis-1,2-dimethylcyclopropane be diastereotopic at every if the other groups attached to C3 room the same? (C1 and C2).

Hard to explain what I mean over paper but probably someone just provided an explanation for how they contain these signals would certainly clear it up for me.


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· 4y · edited 4y
BSc Chemistry
imagine the molecule in 3D.

i drew it because that you as best as i conveniently could, but its important to realise the H atoms are actually behind eachother.:

https://i.gyazo.com/96d3968e90ad4ef61807ffe611b73152.png

I significant one H with a plus and also another with a minus. This is no their charge but a means to determine them for now as i had no proper drawing tool obtainable to offer them numbers.

now if you look in ~ it you view that because that the cis version H+ is actually on the same side as both the the methyl substituents. This method it "feels" them rather well, together opposed come the H- i m sorry is top top the other side of the ring.

for trans, however, both hydrogens "feel" a adjoining methyl team equally, and the peaks will overlap.

if friend replace one of the methyl groups by anything rather though, the H atoms have to again end up different from eachother, castle still room diastereotopic in the regard. Their neighbourhood is just the same in this case.


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· 4y

Why wouldn't the H's on C3 for trans-1,2-dimethylcyclopropane likewise be diastereotopic though, make the link 4 signals?

The test for diasterotopic proton is to merely replace among them v something - let's say a chlorine. Currently replace the other one in a different molecule. Space these two molecules identical? If you've done it for the trans-1,2-dimethylcylopropane, you'll find that you finish up through two molecule that's no distinguishable - revolve one 180 degree and you'll watch that it superimposes the other. Therefore the two protons are homotopic.

Likewise, carry out the very same exercise through the cis- isomer, and also you'll discover you get one molecule with a chlorine ~ above the same side the the ring together the methyl groups, and also one v the chlorine top top the opposite side - 2 diastereotopic protons.


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Op · 4y · edited 4y

Okay im trying to monitor what y'all space saying here however I'm still pretty confused.

Isn't cis-1,2-dimethylcyclopropane meso (because that symmetry)? so if you replaced one of the H's with a Cl wouldn't the molecule still it is in superimposable ~ above its winter image?

I assumed the trans molecule wasn't meso at the same time which would allow the H's to it is in diastereotopic..

See more: Red Rose With Falling Petals Falling Photos And Premium High Res Pictures


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