B, Al and P Flashcards
Aqueous grignards
They exist in equilibrium in solution. The smaller the R group and solvent, the greater the number of interactions between the metal ion and the solvent. Typically it is 4.
Why is boron a strong Lewis-acid
Boron can only form three covalent bonds. Even after these, its octet is not satisfied and there is a empty, valence orbital that can accept electrons
Characteristic of the bridging B-H-B bond
3c, 2e. Three centre and two electron
Uses of hydroboration
Used instead of the acid hydration of alkenes. It gives the hydroxyl group on the least substituted carbon as supposed to the most
How do hydroborates stabilise carbocations
The negative charge on the B atom stabilises the carbocation charge, this allows for the formation of the less stable intermediate during hydroboration
C-B uses in synthesis
These can be converted into C-X bonds
Geometry of the [BH4]- ion
Tetrahedral, sp3 hybridizes
Reactivity of BH4 vs AlH4
AlH4 is more reactive, and hence a stronger reducing agent
Other similarly important B and Al compounds that aren’t the hydrides
The tri-halides. Typically BF3 and ACl3
Typical valence and oxidation conditions of P
typically (III) and trivalent or (V) and pentavalent
Names of the tri and pentavalent phosphorous - oxygen compounds and their structures.
Phosphines and phosphine oxides. Trigonal pyramidal and tetrahedral
Acid/base properties of phosphine
The lone pair on phosphorous acts as a Lewis base
Bond characteristics of the P=O and P=C bond
Not a true double bond, instead a single bond with a formal positive or negative charge
Outline the Wittig reaction
Formation of an alkene and phosphine oxide from a ketone and ylid
Driving force behing the Wittig reaction
The strong P=O bond, approx 500 kJmol-1
