| zero-carbon bridge |
_~^three<arbon bridge |
| four-carbon bridge j [ /
bkyclo(4.3.0]nonane
trans-] ,6-dibromo- 7,7-dimetylo- 2-chloro-
bicyklo[4.3.0]nonan bicyklo[4.1,9]heptan bicyklo[4.2.0]oktan '
bicyklo[2.2.1]- 3-chlorospiro[5.3]nonan hept-2-en