Unsaturated groups vinyl series

The concentration of unsaturated groups in polymers can be determined both by IR and Raman spectroscopy. These groups are susceptible to various chemical reactions, desirable in some cases and hazardous in other cases. The C=C stretch band appears at about 1650 cm" and a series of absorption peaks should appear at 965 cm" (traws-vinylene), 910cm" (vinyl end group) and 730 cm" (cis-vinylene). These absorption bands refer to IR. Raman spectroscopy is, however, more suitable for quantitative analysis of unsaturation. The absorption peaks are stronger than for IR spectroscopy. Polybutadiene shows Raman peaks at 1650 cm" ... 

Further utility of the Andersen sulphoxides synthesis is demonstrated by the preparation of optically active unsaturated sulphoxides which were first prepared by Stirling and coworkers359 from sulphinate 276 and the appropriate vinylic Grignard reagents. Later on, Posner and Tang360 prepared in a similar way a series of ( )-l-alkenyl p-tolyl sulphoxides. Posner s group accomplished also the synthesis of (+)-(S)-2-(p-tolylsulphinyl)-2-cyclopentenone 287, which is a key compound in the chiral synthesis of various natural products361 (equation 159). 

If the alkyl groups in any R SnX4 series are replaced by phenyl, the U9Sn signal moves to lower frequencies (Table XI), which is inconsistent with the greater electron withdrawing capability of a phenyl substituent on tin. Similar effects are found with benzyl, vinyl, and allyl groups (Tables XXX and XXXI) and may be due to the increased polarizability of these unsaturated substituents. (23) This topic is discussed further in Section III.B.3. 

Figure 3. Comparison of the LUMO energy levels for a series of conjugated unsaturated organic molecules and HOMO energy levels for Sn2-. C - vinyl or phenyl Z = electron withdrawing group such as -CHO, -CN etc. (adapted from LaLonde et al. 1987) (29).

Vinyl allyl ethers and allyl aryl ethers are converted by heating to y,6-unsaturated carbonyl compounds and allyl phenols, respectively. The two groups of reactions are mechanistically related, and are referred to as Claisen rearrangements. Claisen rearrangements of allyl aryl ethers have been reviewed and their kinetics are discussed in Chapter 3 Volume 13 of this series. The present discussion is limited to thermal isomerizations of vinyl allyl ethers. 

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