MOLECULAR SYMMETRY IS THE KEY TO:

CLASSIFYING ATOMS AS EQUIVALENT OR NONEQUIVALENT,

 

PREDICTING NUMBERS OF POSSIBLE PRODUCTS IN SUBSTITUTION REACTIONS,

 

AND, UNDERSTANDING PATTERNS IN NMR SPECTRA.

IF IT'S NOT OBVIOUS FROM SYMMETRY, USE THE ULTIMATE TEST OF EQUIVALENCE:

TO SEE IF 2 H'S ARE EQUIVALENT, FIRST SUBSTITUTE ONE WITH A GROUP X AND DRAW THE PRODUCT, THEN SUBSTITUTE THE OTHER WITH X AND DRAW THAT PRODUCT. IF THE TWO PRODUCTS ARE IDENTICAL, THE 2 H'S ARE EQUIVALENT. IF THE TWO PRODUCTS ARE DIFFERENT, THE 2 H'S ARE NONEQUIVALENT.

A NOTE ON ACCIDENTAL EQUIVALENCE:

EVEN THOUGH 2 H'S MAY BE TRULY NONEQUIVALENT, THEY MAY NOT BE DIFFERENT ENOUGH TO GIVE TWO SEPARATE SIGNALS. IN OTHER WORDS THEY MAY HAVE ENVIRONMENTS THAT ARE SO SIMILAR, THEY OCCUR AT THE SAME POSITION.