Group additivity notation

In the meantime, Benson had developed an additive approach to the thermochemistry of molecules, based on the idea that thermodynamic properties like A H29i can, at least to a certain extent, be regarded as the sum of A fH29i values ascribed to constituent parts of the molecule, such as the C-C bond or the -CH2 - group. These constituent values he called bond additivity values or group additivity values. We shall see the distinction below. Although the objective of these calculations is the standard state enthalpy of formation, superscript ° will not be used in the notation because calculated AfH29S values are approximate by definition. 

Figure 2.57 IR spectra showing the v(OH) region of a ceria sample after activation and a series of exposures to H2 at a temperature of 573 K (a), first exposure at 13 kPa of H2 for 0.5 h (b), second exposure at 13 kPa of H2 for 0.5 h (c), and third exposure at 3 kPa of H2 for 0.5 h (d). Roman numerals refer to methoxy species on different types of hydroxyl groups. The notation ll-A has been used because other type II species may be observed in addition. Reproduced from Ref (509).

In Sect. 2.3.2 a single-product heterobimetallic [ W = M, M, M — M ]cBER-(-uNt mechanism was presented for a hydroformylation where PW = 2 simultaneous pathways exist. The updated figure which provides emphasis to constraints is shown in Fig. 14 where additional notation for Gibbs energy of reaction and sets of rate constants fc on the cycle associated with each group are provided. 

The Wiswesser Line Notation (WLN) was introduced in 1946, in order to organize and to systematically describe the cornucopia of compounds in a more concise manner. A line notation represents a chemical structure by an alphanumeric sequence, which significantly simplifies the processing by the computer [9-11], (n many cases the WLN uses the standard symbols for the chemical elements. Additionally, functional groups, ring systems, positions of ring substituents, and posi-... 

It IS convenient m equations such as this to represent generic alcohols and alkyl halides as ROH and RX respectively where R stands for an alkyl group In addition to con venience this notation lets us focus more clearly on the functional group transformation that occurs the OH functional group of an alcohol is replaced as a substituent on car bon by a halogen usually chlorine (X = Cl) or bromine (X = Br)... 

PECH was modified under similar reaction conditions, except that dimethylformamide (DMF) was used as the reaction solvent. In addition, the phase-transfer-catalyzed etherification of the chloromethyl groups of PECH with sodium 4-methoxy -4 -biphenoxide was used to synthesize PECH with direct attachment of the mesogen to the polymer backbone. Similar notations to those used to describe the functionalized PPO are used for functionalized PECH. In this last case, PPO was replaced with PECH. Esterification routes of both PPO and PECH are presented in Scheme I. 

Frankland s notation was a big step toward showing how atoms or groups of atoms are arranged in space and how molecules can combine and function. In addition, it reduced student learning time by two-thirds. 

Mass spectroscopic analysis of the gas phase revealed that 53 is formed with the concomitant generation of H2. Based on the proposed catalytic cycle for silyUbrmylation (Scheme 6.12), the formation of 53 and 54 can be explained by the intervention of 55 (n=2), which plays a pivotal role in the differentiation between intramolecular nucleophilic attack of the hydroxy group and reductive elimination of 54. Thus, the addition of base is believed to accelerate the conversion of 55 to the rhodate anion 56. This notation is supported by the fact that the introduction of a strong base such as DBU is advantageous for the selective formation of a lactone framework. 

The increase in coordination around Tiiv could take place by the simple addition of H2O to Tilvor as a result of hydrolysis of Ti—O—Si bonds and formation of TiOH groups, followed by the addition of H20 to the TiOH groups. Ti02 exhibits little tendency to form surface hydroxyl groups, but could be forced to do so by the unusual condition in which titanium is present in titanium silicates. The steric hindrance of the crystalline lattice prevents Tilv from acquiring the same regular octahedral coordination that it assumes in many of its compounds. A shorthand notation of H20 on Tilv will be used to indicate the increased coordination ... 

Tables 2.6 through 2.10 (see pp. 75-83) list AH° values for a large number of groups (see Section 9.1 for additivity data for radicals). In these tables, Cd refers to a carbon that is forming a carbon-carbon double bond. The notation Cd-(H)2(Cd) is shortened to Cd-(Ha), since all carbon-carbon double bonds are between two sp2 carbons. Similarly, Ct-(X) refers to a carbon triply bonded to another sp carbon and to an X ligand CB-(X) refers to an aromatic ring carbon bonded to two other ring carbons and to a substituent X and Ca refers to the central carbon of the allenic group C=C=C. Other group abbreviations are noted at the end of the appropriate table.

This chapter begins with an introduction to the basic principles that are required to apply radical reactions in synthesis, with references to more detailed treatments. After a discussion of the effect of substituents on the rates of radical addition reactions, a new method to notate radical reactions in retrosynthetic analysis will be introduced. A summary of synthetically useful radical addition reactions will then follow. Emphasis will be placed on how the selection of an available method, either chain or non-chain, may affect the outcome of an addition reaction. The addition reactions of carbon radicals to multiple bonds and aromatic rings will be the major focus of the presentation, with a shorter section on the addition reactions of heteroatom-centered radicals. Intramolecular addition reactions, that is radical cyclizations, will be covered in the following chapter with a similar organizational pattern. This second chapter will also cover the use of sequential radical reactions. Reactions of diradicals (and related reactive intermediates) will not be discussed in either chapter. Photochemical [2 + 2] cycloadditions are covered in Volume 5, Chapter 3.1 and diyl cycloadditions are covered in Volume 5, Chapter 3.1. Related functional group transformations of radicals (that do not involve ir-bond additions) are treated in Volume 8, Chapter 4.2. 

The simple addition reaction in Scheme 19 illustrates how the notation is used. Ester (1) can be dissected into synthons (2), (3) and (4). Synthons for radical precursors (pro-radicals) possess radical sites ( ) A reagent that is an appropriate radical precursor for the cyclohexyl radical, such as cyclohexyl iodide, is the actual equivalent of synthon (2). By nature, alkene acceptors have one site that reacts with a radical ( ) and one adjacent radical site ( ) that is created upon addition of a radical. Ethyl acrylate is a reagent that is equivalent to synthon (3). Atom or group donors are represented as sites that react with radicals ( ) Tributyltin hydride is a reagent equivalent of (4). In practice, such analysis will usually focus on carbon-carbon bond forming reactions and the atom transfer step may be omitted in the notation for simplicity. 

In each column, the symbol for the point group is given in International notation on the left and in Schonflies notation on the right. When n = 2, the International symbol for D2h is mmm. When n is odd, the International symbol for C v is nm, and when n is even it is nmm. Note that n = n/2. In addition to these groups, which are either a proper point group P, or formed from P, there are the three cyclic groups 1 or Ci = E, 1 or Q = EI, and morCs = E a. ... 

---