Whats is the difference between +r effects and - r effects

1.	Whats is the difference between +r effects and - r effects
Answer» Thanks pragati...for nice answer In -R (-Resonance effect) the electron pair transfers to function group or atom .e.g. -Nitrobenzen .In +R (+Resonance effect) e- pair transfer from functional group which can delocalised e- (s).e.g. -phenol What is r -effect???? I studied about I-effect, E-effect,M-effect,H-effect ......but what about r-effect...

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