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I'm considering a problem whereby 1-isopropyl-4-methylcyclohexane with the indicated stereochemistry shown undergoes radical bromination at the indicated position. I understand there are other products produced. However, if the radical initiator (not shown) extracts the hydrogen at the 4 position, then the bromine radical attacks, there will be two distinct products. However, I am having trouble determining if these molecules are chiral? Are they diastereomers to each other?

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Also, as a follow up, how would you name these (reagent + two products) to indicate their stereochemistry?

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  • $\begingroup$ No, they aren't chiral because of symmetry plane, they are cis/trans isomers $\endgroup$ – Mithoron Nov 16 '15 at 21:59
  • $\begingroup$ Mith is right. But that doesn't mean they're not diastereomers though :) $\endgroup$ – orthocresol Nov 16 '15 at 22:06
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They are not chiral because $\ce{C}-4$ is only considered to be bonded to 3 unique groups because the ring is completely symmetrical through $\ce{C}-1$ and $\ce{C}-4$.

As for naming these compounds, the reagent is simple: cis-1-isopropyl-4-methylcyclohexane (or cis-1-(1-dimethylethyl)-4-methylcyclohexane if you're a stickler for the rules).

The products are a little tricker. Let's start with the basics: it is 1-bromo-4-isopropyl-1-methylcylohexane. Now to account for the steric relations of these substituents, label the reference substituent (labeled r) followed by a hyphen and the substituent locator number and name. The relative configuration of other substituents are then reported as cis (c) or trans (t) to the reference substituent.

This means that in the order that you present the products, their names are r-1-bromo-t-4-isopropyl-1-methylcylohexane and r-1-bromo-c-4-isopropyl-1-methylcylohexane.

[Source - (page 1060)]

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  • $\begingroup$ Do you have any references for the naming of the products with the r/s c/t nomenclature? I was trying to work these out myself but hit a brick wall. The only info I had was from March's Advanced Organic Chemistry, but the discussion was incredibly brief. $\endgroup$ – NotEvans. Nov 16 '15 at 22:26
  • $\begingroup$ "if you're a stickler for the rules" - "isopropyl" is (probably) the preferred IUPAC name for $\ce{-CHMe2}$. $\endgroup$ – orthocresol Nov 16 '15 at 22:26
  • $\begingroup$ Yes, it is the preferred name. Maybe I should have said if you're a stickler for systematic names :) $\endgroup$ – ringo Nov 16 '15 at 22:34
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    $\begingroup$ @orthocresol The preferred prefix for $\ce{(CH3)2CH-{}}$ is “propan-2-yl”. The prefixes “isopropyl” and “1-methylethyl” may be used in general nomenclature. Besides, the stereodescriptors cis and trans are not used in preferred IUPAC names, but they may be used in general nomenclature. $\endgroup$ – Loong Nov 16 '15 at 22:45
  • $\begingroup$ @Loong in the source that I linked, cis-inositol is listed as a a preferred IUPAC name. I think cis-trans nomenclature is preferred less than other stereodsicriptors, but when they are not an option cis and trans are in fact used. $\endgroup$ – ringo Nov 16 '15 at 22:56

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