amoroso 1 from chatgpt Flashcards
Why can’t methyl lithium form simple 2-center-2-electron bonds to satisfy the octet rule?
Because Li and CH₃ don’t share enough electrons to complete octets, so it forms multi-centered oligomers like tetramers.
What does the solid-state structure of MeLi look like?
A distorted cube (tetramer), with Li and CH₃ alternating at corners.
What type of bonding explains MeLi’s structure?
Three-center, two-electron bonding (delocalized bonding around Li atoms).
What kind of structure does trimethylaluminium adopt?
A dimer with bridging methyl groups.
What does the NMR of Al₂Me₆ show at room temp and low temp?
One signal at room temp due to fast exchange; two signals at –40°C (2:1 ratio) due to slow exchange between bridging and terminal methyls.
How is B₂H₆ synthesized?
By reacting NaBH₄ with I₂.
What makes B₂H₆ different from a simple ethane-like molecule?
It’s electron-deficient, can’t form enough 2-electron bonds, and forms 3-center-2-electron B–H–B bridges.
How does IR and electron diffraction support the structure of B₂H₆?
They confirm a C₂v geometry with bridging hydrogens, not a simple ethane-like structure.
How does the NMR of B₂H₆ reflect its structure?
Shows distinct environments for bridging and terminal hydrogens; coupling patterns reflect 3-center bonding.
Why is diborane considered electron deficient?
It has only 12 valence electrons but appears to have 8 bonds, which would need 16 electrons.
What bonding model explains electron-deficient compounds like B₂H₆?
Multi-center bonding models like 3-center-2-electron bonds, developed further by Lipscomb.
How does diborane form larger boron clusters?
Through loss of H₂ and reaction with BH₃ units to form species like B₃H₉, B₄H₁₀, etc.
What was the significance of boron hydride research in the 1950s–60s?
Interest in rocket fuel due to high hydrogen content and energy density.
How were early boron hydrides synthesized?
By reacting metal borides with acids (as discovered by Stock).
What do Wade’s rules help predict?
The structure/geometry of boron clusters based on skeletal electron pairs (SEPs).
What structure does a cluster with 6 borons and 7 SEPs form?
Closo (complete polyhedron).
What structure would a B₅H₉ molecule form based on Wade’s rules?
Nido (1 vertex missing from a closo shape).
Why is 10B used in brain cancer treatment?
It absorbs neutrons, releasing alpha particles (He) and Li ions that kill tumor cells with minimal collateral damage.
What makes neutron capture therapy effective inside the skull?
Neutrons penetrate tissue, but only react with 10B, confining radiation to cancer cells.
