Elimination reaction with 1,2-dibromo-4-methylcyclohexane

I was doing a question from a practice exercise on the topic of elimination reactions and alkene synthesis. It is shown below:


[![enter image description here](https://i.stack.imgur.com/i18sY.png)](https://i.stack.imgur.com/i18sY.png)


I predicted that the product would be 1,2-diiodo-4-methylcyclohexane because I thought the reaction conditions favoured substition with iodide via the $\ce {S\_N2}$ mechanism. Firstly, iodide is a rather good nucleophile and secondly, the substrate is a secondary alkyl halide. Even if it was not $\ce {S\_N2}$, I would expect perhaps $\ce {S\_N1}$ since iodide is a rather weak base and the conditions do not seem to favour elimination. However, the answer provided is very interestingly, 4-methylcyclohexene. Would someone kindly enlighten me on where I went wrong? 





> 
> Dehalogenation of vicinal dihalides by iodide ion occurs stereospecifically and
>  concertedly via an $\mathrm{E2}$ mechanism. An anti-coplanar arrangement of both bromine atoms is required (see [diagram](https://image.slidesharecdn.com/08alkesynth-120625210757-phpapp01/95/08-alkesynth-23-728.jpg?cb=1340658567) below):
> 
> 
> 


![diagram](https://image.slidesharecdn.com/08alkesynth-120625210757-phpapp01/95/08-alkesynth-23-728.jpg?cb=1340658567)


Since, the given compound is a 1,2-*trans*-dibromocyclohexane, two bromo groups can arrange in 1,2-*anti*-diaxial positions in one of chair confirmations, fulfilling the requirement. It won't be possible if it'd have been a 1,2-*cis*-dibromocyclohexane.


Reference: Structure & Synthesis of Alkenes (Chapter 7): Leroy G. Wade, *Organic Chemistry*; 8th Edn, Pearson Education Limited: Harlow, Essex, UK, 2014. 


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[![Conformation of 1,2 dibromo,4-tertbutyl cyclohexane](https://i.stack.imgur.com/hqLDZ.png%5C)](https://i.stack.imgur.com/hqLDZ.png%5C)


As you can see from above mechanism the dibromo needs to be in an axial positions for elimination


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