Alkenes Infrared Spectroscopy and Mass Spectrometry

CHAPTER 11 Alkenes Infrared Spectroscopy and Mass Spectrometry 

We begin with the names and physical properties of the alkenes and show how we evaluate the relative stability of their isomers. A review of elimination reactions allows us to further our discussion of alkene preparation. 

We also introduce two additional methods for determining molecular structure a second type of spectroscopy—infrared (IR) spectroscopy—and a technique for determining the elemental composition of a molecule— mass spectrometry (MS). These methods complement NMR by ascertaining directly the presence or absence of functional groups and their characteristic bonds (O—H, C=C, etc.), as well as their arrangement in the overall structure. 

In Chapters 11 and 12 we return to the presentation of a new functional group the carbon-carbon double bond. This functional group differs from those seen so far in that it lacks strongly polarized covalent bonds. Instead, its reactivity arises from special characteristics of electrons in so-called bonds. The properties of these electrons and their consequences are discussed in the next chapter. Chapter 11 is restricted to a general description of alkenes as a compound class and a presentation of methods of preparation of double bonds. Most of the reactions are ones you have already seen because the major methods of alkene syntheses are the same elimination reactions of alcohols and haloalkanes that were presented in Chapters 7 and 9. Only some finer details have been added. 

This chapter also introduces infrared spectroscopy, a useful tool for qualitative identification of functional groups, and mass spectrometry, the best method for determining molecular composition. 

11-5 Hydrogenation Relative Stability of Double Bonds Comparing alkenes and alkanes. 

11-7 Alkenes by Dehydration of Alcohols Mostly review material in these two sections. 

Little needs to be added to the text descriptions for these two topics. The nomenclature rules are straightforward. Again, a small number of common names are still in use and must be learned. However, the systematic nomenclature is logical and easy to master. Note that alkenes, like cyclic alkanes, have two distinct sides, and therefore substituents may be either cis or trans to each other. For alkenes, however, the cis and trans designations should be restricted to molecules with exactly two substituents, one on each of the two doubly bonded carbons. If more substituents are present, the E,Z nomenclature system should always be applied. 

---

Chapter 11 ALKENES INFRARED SPECTROSCOPY AND MASS SPECTROMETRY... 

---