Is BF3 an electrophile

• hoay

  7 Mar 16, 04:38

  In BF3  Boron atom has 6e can we call it an electrophile? 

  Secondly why LiAlH4 is more reactive than NaBH4 as reducing agent.

• UltimaOnline

  7 Mar 16, 05:39

  Originally posted by hoay:

  In BF3  Boron atom has 6e can we call it an electrophile? 

  Secondly why LiAlH4 is more reactive than NaBH4 as reducing agent.

  
  Yes, the BF3 molecule is an electrophilic Lewis acid (with the B atom being the dative bond acceptor). The term "Lewis acid" refers to its propensity to accept dative bonds, while the term "electrophile" refers to its propensity to seek electrons, so both terms are closely related, but not technically the same. In addition, the terms "nucleophile" and "electrophile" are by convention, favored for use specifically in Organic Chemistry, while the terms "Lewis base" and "Lewis acid" are overarching archetypes across all branches of Chemistry. For Cambridge A level Chemistry purposes, exam-smart students are advised to combine both terms (ie. any and all relevant terms or keywords for all questions in general) to secure the marks, even if Cambridge is usually reasonable and will accept either term.

  For 2 closely related reasons. Firstly, because Al has a larger atomic radius than B, and thus polarizability of the electron bond pairs of the H- hydride ions increase with increasing distance from the central 'cationic' atom, as predicted by Coloumb's law, and also due to increasing shielding effect from larger number of inner shell electrons. Secondly, the lattice dissociation enthalpy for the covalent bonds with the hydride ions becomes less endothermic (ie. bond weakens) as bond length increases from BH4- to AlH4-, due to less effective overlap of more diffused electron shell orbitals involved in forming the sigma bonds. For both reasons above, concordantly and consequently, LiAlH4 is a significantly more effective delivery agent of H- hydride ion nucleophiles, compared to NaBH4.

• UltimaOnline

  7 Mar 16, 19:49

  In case you were asking *why* BF3 is an electrophilic Lewis acid, it's because the B atom only has 3 bond pairs + 0 lone pairs, and thus lacks a noble gas stable octet valence shell electron configuration, and thus has a propensity to accept a dative bond to achieve a stable octet electron configuration.