Sp hybridized C-B compounds

The most important substrates for substitutions of this type are alkenyl and aryl triflates, bromides, or iodides (Sections 16.1-16.4). The most important organometallic compounds to be introduced into the substrates contain Cu, Mg, B, Zn or Sn. The metal-bound C atom can be sp2-, sp2-, or. sp-hybridized in these compounds, and each of these species, in principle, is capable of reacting with unsaturated substrates. Organocopper compounds often (Section 16.1, 16.2), but not always substitute without the need for a catalyst (Section 16.4.5). Grignard compounds substitute in the presence of catalytic amounts of Ni complexes (Section 16.3), while organoboron (Section 16.4.2), organozinc (Section 16.4.3) and organotin (Section 16.4.4) compounds are typically reacted in the presence of Pd complexes (usually Pd(PPhj)4). 

An sp hybridized C—Cl bond is more polar than an sp hybridized C-CI bond, (a) Explain why this phenomenon arises, (b) Rank the following compounds in order of increasing boiling point. 

A molecule containing one 7t-bond as part of a C=C unit is called an alkene (see Chapter 5, Section 5.1). When a molecrde contains two 7i-bonds in two C=C units, it is called a diene. There are three fundamental structmal variations for a diene (a) those where the C=C units are separated by sp hybridized atoms, (b) those where the C=C units are connected together to form a C=C-C=C unit, and (c) those that contain two 7i-bonds that share an sp hybridized atom. Compounds (a) are called nonconjugated dienes using the standard nomenclature rules for alkenes introduced in Chapter 5, an example is 1,5-hexadiene (1). Compounds (b) are called conjugated dienes, illustrated by 1,3-hexadiene (2). Note that 2 contains an E double bond (see Chapter 9, Section 9.4.3) and the name must reflect this structural feature. Therefore, 2 is l,3 -hexadiene. 

Compare, for example, the IR spectra of 5-methyl-2-hexanone (A) and ethyl propanoate (B) in Figure 13.9. The IR spectra look similar in their functional group regions because both compounds contain a carbonyl group (C=0) and several sp hybridized C-H bonds. Since A and B are different compounds, however, their fingerprint regions look very different. 

When a nucleophile adds to a carbonyl group, the hybridization of the carbonyl carbon changes from sp in the carbonyl compound to sp in the addition product. In Section 17.5, we saw that a compound that has an sp carbon bonded to an oxygen atom generally will be unstable if the sp carbon is also bonded to another electronegative atom. Therefore, if the nucleophile that adds to the aldehyde or ketone is one in which Z is not electronegative (Z is an H or a C nucleophile), the tetrahedral addition product will be stable. It will be an alkoxide ion that can be protonated either by the solvent or by added acid. (HB is any species that provides a proton =B is any species that removes a proton.)... 

Folberth [6] has noted that the sp hybridization of the valence electrons in A B C/ compounds is energetically advantageous only if the difference in the polarizations of the A-C and B-C bonds is not too great. 

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