5/7-hybridized carbon

This chapter discusses the chemistry of 1,3-dioxanes, -oxathianes, -dithianes, their unsaturated and benzo-fused derivatives, and their tautomers. All possible degrees of unsaturation in the six-membered ring, from zero to four 5/7 -hybridized carbon atoms, are included. Following a brief treatment of theoretical, structural, and spectroscopic studies, the reactivity of the different ring systems is examined, categorized by the formal degree of unsaturation. 

Simplest alkene is C2H4 (ethylene), which is described as containing 5/7 hybridized carbon atoms... 

Alcohols are organic compounds that contain a hydroxyl group (OH) attached to a saturated carbon. A saturated carbon is an 5/7 -hybridized carbon, i.e., a carbon that is bonded to other atoms only through single bonds, no double or triple bonds. The alcohol family has the general formula R—OH and the first member is CH3OH lUPAC name methanol common name methyl alcohol. Other alcohols are... 

The positive charge is shared equally by the three carbons indicated. Thus the two carbons ortho to the 5/7 -hybridized carbon and the one para to it each bear one third of a positive charge (+0.33). None of the other carbons is charged. The resonance picture and the simple MO treatment agree with respect to the distribution of charge in cyclohexadienyl cation. 

When in a set of ZW groups, W is CH2, CH, C, C=0, C6H4, CH==CH, or C C, no problem arises as the hybridized carbon atom our previous results suggest that the delocalized effect is insignificant. Thus, we expect that for (T/,zch2 <1 OdZCH2>... 

Notice that all the examples in Table 8.1 involve alkyl halides, that is, compounds in which the halogen is attached to an 5/7 -hybridized carbon. Alkenyl halides and aryl halides, compounds in which the halogen is attached to 5/7 -hybridized carbons, are essentially unreactive under these conditions, and the principles to be developed in this chapter do not apply to them. 

The pattern is repeated in higher alkynes as shown when comparing propyne and propene. The bonds to the p-hybridized carbons of propyne are shorter than the corresponding bonds to the 5/7 -hybridized carbons of propene. 

Figure 10.1 gives an orbital overlap view of bonding in allyl cation. The planar structure of H2C=CHCH2" (Figure 10.1a) provides a framework that allows for continuous overlap of the 2p orbitals of the three adjacent 5/7 -hybridized carbons (Figure lO.lfo and c). Until now, we have only seen rr orbitals involving two adjacent carbons. Conjugated systems are characterized by extended rr orbitals that encompass three or more atoms. The electrostatic potential map (Figure 10.Id) shows the equal sharing of positive charge between the first and third carbons of 2C...

This greater 8 2 reactivity of allyl chloride results from a combination of a steric effect and an electronic effect. The —CH2CI group is less crowded in allyl chloride, where it is attached to a trigonal planar 5/7 -hybridized carbon of H2C=CH—, than in 1-chloropropane, where it is attached a tetrahedral 577 -hybridized carbon of CH3CH2—. 

Some of these characteristic absorptions are reflected in the IR spectra of eight functional-group classes in Figure 13.36 alcohol, nitrile, carboxylic acid, ketone, ester, ether, amine, and amide. None of the specific compounds represented contains hydrogens bonded to 5/7 -hybridized carbon, so all of the C—H absorbances lie below 3000 cm The compounds are related in that all have an unbranched six-carbon chain and, except for the peaks associated with the functional group, their spectra are similar, though not identical. 

A considerable body of data is available on the acidity of substituted benzoic acids. Benzoic acid itself is a somewhat stronger acid than acetic acid. Its carboxyl group is attached to an 5/7 -hybridized carbon and ionizes to a greater extent than one that is attached to an 5p -hybridized carbon. Remember, carbon becomes more electron-withdrawing as its 5 character increases. 

As we ve seen on a number of occasions, bonds to 5/7 -hybridized carbon are shorter than those to 5/7 -hybridized carbon, and the case of phenols is no exception. The carbon-oxygen bond distance in phenol is slightly less than that in methanol. 

TT bond In alkenes, a bond formed by overlap of p orbitals in a side-by-side manner. A tt bond is weaker than a a bond. The carbon-carbon double bond in alkenes consists of two 5/7 -hybridized carbons joined by a CT bond and a tt bond. 

Vicinal diol Compound that has two hydroxyl (—OH) groups on adjacent 5/7 -hybridized carbons. 

Of the 5p -hybridized carbons, C-1 is the most shielded because it is bonded to only one other carbon. The least shielded carbon is the ring carbon to which the side chain is attached. It is the only 5/7 -hybridized carbon connected to three other carbons. 

The latter reaction is an example of the di-n-methane rearrangement This rearrangement is a very general reaction for 1,4-dienes and other systems that have two % systems separated by an 5/7 -hybridized carbon atom ... 

The insertion of a carbonyl group in between the 5/7 -hybridized carbon atoms of an alkene can be accomplished through the formation of cyclopropanone thioacetals from the appropriate epoxide or dibromocyclopropane and treatment of these compounds with aqueous trifiuoroacetic acid (Scheme 16), ... 

The fact that a strong base can be used to pull an H off an 5/7-hybridized carbon is another wrinkle that will be explored in upcoming activities. As a preview, note that the resulting acetylide anion is a carbon nucleophile that can be combined with carbon electrophiles to make a wide range of carbon-carbon bonds. The only example of this we have discussed so far is nucleophilic epoxide ring opening. 

---