Question

Which of the following does not exist in free form?

• A. $ B{{H}_{3}} $
• B. $ B{{F}_{3}} $
• C. $ BC{{l}_{3}} $
• D. $ BB{{r}_{3}} $

Answer 1

Answer: (A)

$ B{{H}_{3}} $ does not exist in free form because H-atoms in $ B{{H}_{3}} $ have no free electrons to form $ p\pi -\rho \pi $ back bonding and thus boron has incomplete octet and hence $ B{{H}_{3}} $ molecule dimerise to form $ {{B}_{2}}{{H}_{6}}. $