Treating a hindered alkene such as 2-methyl-2-butene with BH3: THF leads to the for- mation of a dialkylborane instead of a trialkylborane. When 2 mol of 2-methyl-2-butene is added to 1 mol of BH3, the product formed is bis(3-methyl-2-butyl)borane, nicknamed "disiamylborane." Write its structure. Bis(3-methyl-2-butyl)borane is a useful reagent in certain syntheses that require a sterically hindered borane. (The name "disiamyl" comes from "disecondary-iso-amyl," a completely unsystematic and unacceptable name. The name "amyl" is an old common name for a five-carbon alkyl group.)