- ben zo atic ▁( left , ▁below ) ▁& ▁ 6 - ben zo atic ▁( right , ▁below ) ▁ ▁Com parison ▁of ▁trop ane ▁ring ▁versus ▁the ▁nor born ane ▁in ▁overlay , ▁with ▁contrast ▁of ▁ben zo yl ▁branch ▁in ▁its ▁configuration ▁of ▁how ▁it ▁l ays ▁extended ▁out ▁from ▁body ▁of ▁either ▁main ▁ring ▁type ▁( sh own ▁twice ▁in ▁different ▁colors , ▁for ▁visibility , ▁above ) ▁▁ 6 / 7 ▁trop ane ▁position ▁m eth ox yc oca ine ▁& ▁m eth ox yp se ud oc oca ine ▁analog ues ▁▁ 3 β - position ▁ 2 ′ — ( 6 ′ ) ▁& ▁ 2 β - subst itution ▁combination ▁analog ues ▁▁ ɑ For ▁disp lacement ▁of ▁[ 3 H ] par ox et ine ▁( 5 - HT T ▁& ▁N ET ) ▁b For ▁disp lacement ▁of ▁[ 3 H ] nis ox et ine ▁( 5 - HT T ▁& ▁N ET ) ▁▁ 3 β - Car b amo yl ▁analog ues ▁ ▁Ph en yl ▁ 3 - position ▁link age ▁substitution s ▁See : ▁List ▁of ▁ph eny lt rop anes ▁( Many ▁ph eny lt rop anes ▁are ▁derived ▁from ▁c oca ine ▁met abol ites , ▁such ▁as ▁m eth yle c gon id ine , ▁as ▁prec urs ors . ▁Where as ▁fully ▁synth etic ▁methods ▁have ▁been ▁de vised ▁from ▁the ▁starting ▁material ▁of ▁vin yl car ben oid s ▁& ▁p yr