Is (2R,3S)-2,3-dichloropentane optically inactive? Two confusing thing about (2⁠R,3⁠S)-2,3-dichloropentane:


The 2 stereocenters have opposite absolute configuration.
But there is no plane of symmetry.


So, is (2⁠R,3⁠S)-2,3-dichloropentane optically inactive? 

(This is actually a follow-up question of:
Monochlorination of 2-chloropentane and possible enantiomer products)
To have an optically inactive meso compound with two chiral centers:

1)  the chiral centers must have opposite configuration

2)  the chiral centers must have the same set of fragments bonded to them

Among other things the 2 carbon has a methyl group bonded to it versus the 3 carbon having an ethyl group instead.  You do not satisfy (2), so you do not have the symmetry required for a meso compound, and the molecule is still chiral and optically active.