Draw the Newman projections for the anti and gauche forms of 1,2-dibromoethane.

Question

Draw the Newman projections for the anti andgauche forms of 1,2-dibromoethane. The molecule has adipole moment of 1.0 D.

a) Which form is responsible for the molecular dipole(gauche/anti)?
1---Select---antigauche

(b) Which conformation of 1,2-dibromoethane is present in thegreatest amount at equilibrium (eclipsed/gauche/anti)?
2---Select---antigaucheeclipsed

(c) Which of the following compounds has the larger energy barrierto internal rotation about the central bond? (Hint: compare bondlengths!)

3 (CH3)3C-C(CH3)3
(CH3)3Si-Si(CH3)3

I have no idea how to start this. Can someone help me figureout how to do this?
3

Explanation / Answer

A.) Think about the definition of a dipole... this meansthat there is a positive end and a negative end (bothpartially). Therefore, the gauche interaction will be whatcauses the dipole (both Br atoms next to each other). This isbecause Br pulls electrons to itself more than C does. B.) The anti conformation will be more abundant atequilibrium because there is no dipole and there is less stericinterference. C.) The compound containing C-C bonds would be higher inenergy while rotating becasue Si is larger and therefore, seperatesthe t-butyl groups further apart. (this one I am not 100%sure of) Hope this helps!

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