Four of the following five are alike in a certain way and so form a group. Which is the one that does not belong to that group?

The data given to us is -
Eight friends L, M, N, O, P, Q, R and S are sitting around a square table in such a way that four of them sit at four corners of the square while four sit in the middle of each of the four sides. The ones who sit at the four sides face outside while those who sit in the middle of the sides face the centre.
• Only one person sits between L and Q. L sits at middle of one of the series.
• O sits to the immediate right of Q.
• Both R and S are immediate neighbours of L.
• M sits second to left of N.
• N is neither an immediate neighbour of Q nor S.

This can be intrepreted in diagramatic form as:

R, S, O and P sit at the corners of the table.
L sits at middler of side.