Constitutional isomers features

Constitutional isomers may differ in ways other than the branching of their carbon chain. They may differ in the position of a double bond or other group or by having a ring or some other feature. Notice how the following constitutional isomers all differ by the ways in which atoms are bonded to other atoms. (Check the number of hydrogens bonded to each carbon.) These compounds are not isomers of the pentanes just shown, however, because these have a different molecular formula (C5H10). 

Ru(tpy)2] + units are present in the branches of dendrimers 24 and 25, which have identical molecular formula and are the first example of dendritic constitutional isomers [105]. These isomers feature similar solubility and decomposition temperature, whereas the electrochemical behavior (in acetonitrile), due to the four... 

The first three chapters constitute a review of bonding and an introduction to organic compounds. Functional groups are introduced. Resonance is covered extensively, and numerous examples are provided. Acid-base chemistry is discussed in Chapter 4, and this reaction is used to introduce many of the general features of reactions, including the effect of structure on reactivity. Nomenclature of all of the functional groups is covered in Chapters 5 and 12. In this edition, stereochemistry is covered in two chapters to break up the material Chapter 6 discusses cis trans isomers and conformations, and Chapter 7 addresses chiral molecules. 

The constitution of the angular syn-bisdienophile 74 (see Scheme 20) maintains the bicyclic nature of the two dienophilic units. However, the [a,c]-fusion present in the phenanthrene constitution reduces the end-to-end symmetry of the rc-systems, rendering the two olefinic carbon atoms in each dienophilic unit constitutionally-heterotopic. The effect of this reduction in the symmetry of the 7t-systems in 74 upon the diastereoselectivities exhibited in its cycloadditions was of considerable interest to us. Furthermore, the incorporation of two phenanthrene units into a macropolycyclic belt could ultimately lead to the preparation of an angular isomer 70 of [12]cyclacene 50 (Fig. 20). Compared with [12]cyclacene 50, the angular isomer 70 has some appealing electronic features associated with it. 

A substantial step towards the understanding of the physical, chemical, or biological properties of a molecule is to study and analyze its spatial shape. Besides the constitution, a major shape-determining feature is the configuration of a molecule, i. e. the stereochemistry. Furthermore, molecular chirality plays a major role in many areas of chemistry. Enantiomers often exhibit quite different physical, chemical, and biological properties. The exploration of the configurational space of a molecule and the analysis of the various isomers a molecule can adopt is therefore of great importance. 

All constitutive elements of a compound having been duly considered in compliance with the existing rules, still another set of descriptors has to be envisaged to account properly for all stereochemical features involved. Definitive status has already been attained by the rules for characterizing cisitrans isomers, stereogenic (formerly asymmetric) centers, and exolendo relationships in bicyclic compounds, as will be outlined in subsequent sections. A unified procedure for the treatment of other stereogenic units will be given at the end of this chapter. 

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