[IslandHead]

In the first chapter of Solomon's text book there are exercises for resonance structures. One of the answers to one of the exercises suggests that 1-bromoethene  has resonance structures.

Looking at the image above (from wiki), I don't understand how having a double bond on an halide and introducing charges on the carbon and halide is a meaningful structure. The answer to the question suggests hybridized bonds, but I don't see a need for them. It doesn't appear to need a resonance structure....

I also didn't get this resonance structure
[ CH3-S+=CH2  :resonance:CH3-S-CH2+]
And the answer is with a hybridized bond between the sulfur and the carbon. I don't understand why this would be the case. I didn't think that the structure with the charged carbon would be a meaningful resonance structure, and that the sulfur given its size would be better able to hold the charge.

[orgopete]

There is a difference between "greatest contributor" and other resonance forms. It is true that the greatest contributor for vinyl bromide is as drawn and the uncharged form of methyl vinyl thio ether is a greater contributor. However, if you were to perform reactions and look at how electrons behave, then you would become convinced that the electrons do not remain localized in the greatest contributor. That is all the problem is teaching. If there are non-bonded electrons, they can interact with neighboring pi-electrons. The interactions are referred to as resonance structures.

[Vidya]

I also didn't get this resonance structure
[ CH3-S+=CH2  :resonance:CH3-S-CH2+]
And the answer is with a hybridized bond between the sulfur and the carbon. I don't understand why this would be the case. I didn't think that the structure with the charged carbon would be a meaningful resonance structure, and that the sulfur given its size would be better able to hold the charge.
[/quote]
All resonance structures are not meaningful but we can not deny possibility of delocaliztion of electron density from S to CH2+ and may be it will be less as we are trying to place + charge on electronegative atom S.So it is not an important structure but it is a resonating structure.

[james_a]

Remember that the "positive charge" on sulfur here is in fact a formal charge, rather than representing true electron deficiency. It's easy to get tripped up with this.
The real stability of the resonance structure with the double bond to sulfur is that all components possess a full octet of electrons, whereas in the form CH3S-CH2+ we have a carbon with only six valence electrons.