Structure of 2-Oxaindan Spiropyrans

The conformations of the 2-oxaindan spiropyrans of SP14-SP17 have been investigated.58 

Tabic 2. Main Structural Parameters of 2-Oxaindan Spiropyrans 

407(3) A] compared to the normal length of a C-0 bond in five-membered heterocycles (1.426 A).59 As the C(22 )-0(l) bond length increases, the C(22 )-0(2) bond has a tendency to be shortened whereas the 0(2)—C(13) bond in these SPs remains elongated (see Table 2). 

These interactions are weaker in SP14-SP17 than in SP1-SP11, which contain different heteroatoms (O and N). This can also account for the lesser elongation ofthe Cspjro—0(1) bond in SP14—SP17. 

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