dimethyl ether bond angle question!

[leia03]

Can someone explain why bond angle at oxygen in dimethyl ether is larger than the one water(105)?
Explanation said that the bond angle is greater compared to one in water due to van der waals forces between alkyl groups. I am confused! Shouldn't the angle be smaller than water since interaction pulls alkyl groups closer?

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[gnleff]

You should think of it this way. The hydrogens on water are much smaller than the two methyl groups on the dimethyl ether.

Since everything is single bonded we can assume free rotation. Because the methyl groups are bigger they have a higher chance of colliding into each other more than the two small H's on water. So therefore they have a larger bond angle because by van der waals forces they are pushed away from each other more than the H's.