Question 9.SE.3: Eyedrops for dry eyes usually contain a water-soluble polyme...
Eyedrops for dry eyes usually contain a water-soluble polymer called poly(vinyl alcohol), which is based on the unstable organic molecule vinyl alcohol:
\begin{matrix} H— \overset{..}{\underset{..}{O }} — \overset{\underset{|}{H} }{C}=\overset{\underset{|}{H} }{C}—H\end{matrix}
Predict the approximate values for the H—O—C and O—C—C bond angles in vinyl alcohol.
Analyze We are given a Lewis structure and asked to determine two bond angles.
Plan To predict a bond angle, we determine the number of electron domains surrounding the middle atom in the angle. The ideal angle corresponds to the electron-domain geometry around the atom. The angle will be compressed somewhat by nonbonding electrons or multiple bonds.
Solve In H—O—C, the O atom has four electron domains (two bonding, two nonbonding). The electron-domain geometry around O is therefore tetrahedral, which gives an ideal angle of 109.5°. The H—O—C angle is compressed somewhat by the nonbonding pairs, so we expect this angle to be slightly less than 109.5°.
To predict the O—C—C bond angle, we examine the middle atom in the angle. In the molecule, there are three atoms bonded to this C atom and no nonbonding pairs, and so it has three electron domains about it. The predicted electron-domain geometry is trigonal planar, resulting in an ideal bond angle of 120°.
Because of the larger size of the C=C domain, the bond angle should be slightly greater than 120°.