Carbon compounds correlation plots

The exchange of a considerable number of linear, branched-chain, and cyclic alkanes have been studied (5i). The exchange rate increases with increase in the carbon chain length forn-alkanes (methane to hexane). It is found that there is a linear correlation between the logarithm of the exchange rate and the ionization potential of the alkane (Fig. 5 n-alkanes are plotted as circles). This correlation extends to aromatic compounds (Fig. 5 aromatic compounds are plotted as squares) and is evidence that alkanes and aromatic compounds react by a common mechanism. Indeed, the least reactive aromatic, benzene, is only about... 

The progress in NMR hardware to support the structure elucidation of limited quantity samples allowed to exploit the ADEQUATE experiment to a greater extent [2,93,94]. The advantage of the ADEQUATE pulse sequence originates from C-C magnetization step transfers that allow to specifically differentiate between Jch and Jch bonds which is not possible from HMBC-based experiments. It also includes connectivity information to non-protonated carbon atoms. Thus, multiplicity-edited H-C HSQC and 1,1-ADEQUATE experiments were co-processed to yield a C—C correlation plot [28]. The map was diagonally symmetric in case of adjacent Jcc-coupled protonated carbons and asymmetric in case of Jcc between protonated and quaternary carbons. It was emphasized that the latter responses were observed at the C shift of the protonated carbon in the FI direction and the correlation at the C shift of the quaternary carbon in the F2 dimension, cf. exemplarily for the methylene Cl 1 and the carbonyl CIO in Fig. 5.12. The well-known compound strychnine served as proof-of-principle for the HSQC-1,1-ADEQUATE. 

I have registered his Nhq values (for 20 C, 1 atm) on the 760 mm Hg horizontal in Fig. 92. Several values cluster on each side of the R-line, and those for benzene and toluene indicate that the JVhq vs Phq plot would be concave upward. The value for ethyl bromide, Nhci = 0.102, gives a line over on the right, near the PhOMe line (see later). Hamai (1935) " looked for a correlation between the solubility of HCl in four halogeno-carbon compounds and the polarity, as measured by the dielectric constant, molecular symmetry, electric moment, and Eotvos constant (see Table 20). 

Fig. 2.60. Deriving the carbon skeleton of an organic compound by DEPT and 2D-IN-ADEQUATE with COSY-like square correlations sample 3-(isopinocampheoxy)-2-methyl-l,3-butadiene, 400 mg in 0.4 mL of hexadeuterioacetone, 100.6 MHz (a) proton-broadband decoupled spectrum (1 scan) (b) DEPT subspectrum of CH carbon nuclei (8 scans) (c) DEPT spectrum with CH, CH3 (positive), and CH2 (negative. 8 scans) (d) 2 D-INADEQUATE experiment of aliphatic carbon nuclei, 256 experiments, 64 scans per experiment. The bicyclic partial structure of the molecule can be derived from the square correlations (e.g.. .. —44.2 — 81.1 —35.6—. ..). A stacked plot of the carbon-proton shift correlation of this sample is displayed on the cover.

The Hammett p and the Tafb-Hammett p can be used to evaluate the partial charge at various positions in the substrate fragment of the transition state. Sometimes deviations from the Taft-Hammett correlations can be used for the same purpose (Kreevoy, 1963b Barlin and Perrin, 1966). The positive charge developed at a particular carbon is thought to be approximately —p l4 5 or — p/3-5 or Ap /5, where Jp 0 is the deviation of a phenyl or vinyl compound from a Taft-Hammett plot. 

FIGURE 10. Plot of log ( MeOH/M-1 s 1) vs. Sag for the reaction of carbon-substituted 1,1-dimethylsilenes (2b, 6, 8, 23 and 85a-c) in hexane solution at 23 °C. Compound 6 is excluded from the correlation. Reproduced with permission from Reference 111. Copyright 1999 American Chemical Society... 

McGuire and Suffet [728] proposed the calculated net adsorption energy concept which is based on the solubility parameter of the adsorbate. They justified their approach by noting that the interactions involved in the adsorption of nonpolar and polar compounds onto a nonpolar [activated carbon] surface are, for the most part, governed entirely by the dispersion forces. Their results are summarized in Fig. 31. Even on a log-log plot, the r correlation coefficient is only 0.7. The authors cautioned against extrapolating such a correlation to predict the adsorption capacities of other neutral organic compounds. Clearly, incorporation of model parameters that quantify the chemistry of the carbon surface is necessary. 

Another procedure based only in part on the additivity properties of the values for AH and AS° is based on correlation equations for a series of homolog compounds or of compounds containing a repetitive unit (such as polymers). Since the compounds in a homolog series differ by the same fragment, it can be expected that the values in a series is linear The data used for generating the correlation equation can be either experimental or calculated values of a thermodynamic parameter. As an example, a set of experimental and calculated values for the heats of formation AHf for the series of saturated normal hydrocarbons CnH2n.,2 are plotted as a function of carbon number in Figure 2,2.4. 

Similar correlation equations can be established for other compounds, including free radicals. Since fewer experimental data are available for free radicals or for a series of less common compounds, calculated values can be very helpful for obtaining correlation equations for AH ° and ASf° values (in the case of free radicals open shell MO calculations are necessary). Since many thermodynamic values for chemical reactions are calculated as the difference between the parameters for the forward reaction and those for the reverse reaction (see e.g. rel. 2.2.34), the errors between calculated and experimental thermodynamic parameters may be in part compensated such that the final calculated results are in good agreement with the experiment. However, the compensation may depend on the parameterization of the calculation procedure. For example, the calculated and experimental data for aH° for the series of normal 1-olefins C H2n are plotted as a function of carbon number in Figure 2.2.6. The calculation has been done using MOPAC-7 MO calculation package [22]... 

The chemical shifts of the characteristic carbon signals in acyclic terpenes, polyprenols, and cis-trans isomerized poly-isoprenes are plotted in Fig. 3. Here, the chemical shifts are correlated using the w C-5 methyl carbon signal at 17.66 ppm as an internal standard (except for isomerized polyisoprenes) in order to compensate for the effect of solution concentration. It is clear that these chemical shifts are independent of the chain length of the compounds and can be used for the determination of the arrangement of isoprene units as well as the terminal units in various isoprenoid compounds (8). 

Curved Brpnsted plots or other structure-reactivity correlations are often taken as evidence for changes in transition-state structure with changing properties of the reactant that might be described by the Marcus equation (24) or other equations. However, it is important to evaluate other possible explanations for such curvature, including solvation effects that could decrease the reactivity of basic nucleophiles without any change in the structure of the transition state for nucleophilic attack. For example, solvation effects could provide a relatively simple explanation for the curvature of structure-reactivity correlations for reactions of basic oxygen anion nucleophiles with acyl compounds and carbon acids. 

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