What is the measurement of C-O-C bond angle in methoxymethane?

The correct answer is Option (2) → 111.7°

Methoxymethane (dimethyl ether, CH₃–O–CH₃) contains an oxygen atom bonded to two carbon atoms and having two lone pairs.

Hybridisation of oxygen = sp³

So ideal tetrahedral angle = 109.5°

But actual angle depends on electron pair repulsion.

Lone pair–bond pair repulsion > bond pair–bond pair repulsion

Due to repulsion between lone pairs and bond pairs, the bond angle slightly deviates from the ideal tetrahedral angle (109.5°). Hence bond angle increases. 

Option 1: 108° - This is close to tetrahedral angle but ignores lone pair repulsion effect. Actual angle is larger due to lone pairs.

Option 2: 111.7° Correct. Two lone pairs on oxygen increase repulsion between bonding pairs, expanding the bond angle beyond 109.5°.

Option 3: 90° - Too small. Such angles occur in square planar geometry, not tetrahedral.

Option 4: 60° -Unrealistically small for sp³ hybridisation.