dipole vectors in alkenes

[orangepopsicle]

Hey guys,

Was wondering if anyone could explain to me about how dipole vectors cancel out.

The image below, I am wondering how the trans alkene dipole vectors cancel out. I can only see the dipole vectors from C --> Cl making sense since they are going in opposite directions, but won't the dipole vectors from H --> C combine to make a large dipole moment vector towards the double bond?

Also in the cis alkene, how is the dipole moment of the hot pink arrow determined? Does the C--> Cl dipole vectors cancel out since they are going in opposing directions and the H--> C dipole vectors combine to make the hot pink dipole moment arrow going up?

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[FeralisExtremum]

The difference in electronegativity between C-H bonds is so small that we basically consider it as non-existent. For all practical purposes there is no dipole worth considering between C and H atoms.

But even if you were to count the dipole arrows there: they still cancel out completely in the trans molecule. The dipole in one points up and to the left, in the other it points down and to the right. So even if those two H atoms were say, Br and Br...their net dipoles would still cancel out.

In the cis molecule, you can basically ignore the dipole from the C-H and just look at the C-Cl dipole arrows. One points to the left and the other points towards the right to an equal extent, so horizontally there is no net dipole...but both point upward, so there is a net upward dipole.

 

[orangepopsicle]

thanks for clearing that up!!!