Rule: Any sized rings can be fused in cis but two five-membered rings can be fussed in trans also.
a. No, Four- and five membered rings cannot be fused is trans.
b. Yes, Two five-membered and larger rings can be fused in trans because the trans bounds in the bridgehead C atoms are in a position for a 3C-bridge.
c. No, Three- and six- membered rings cannot be fused in trans. The trans bonds on the bridgehead C atoms are too far apart to be bridged by a single C-bridge.
d. Yes, Any sized rings can be fused cis.
e. Yes, Spiranes for any sized ring are known if they are able to be at right angles.
f. Yes, Two larger rings can be fused in trans.
g. Yes, Any sized rings can be fused in cis.
