Apparent correlation

A comparison of the electron impact (El) and chemical ionization (Cl-methane) mass spectra of 1//-azepine-1-carboxylates and l-(arylsulfonyl)-l//-azepines reveals that in the El spectra at low temperature the azepines retain their 8 -electron ring structure prior to fragmentation, whereas the Cl spectra are complicated by high temperature thermal decompositions.90 It has been concluded that Cl mass spectrometry is not an efficient technique for studying azepines, and that there is no apparent correlation between the thermal and photo-induced rearrangements of 1//-azepines and their mass spectral behavior. 

Figure 14. Plot of the potential of zero charge, Ea=0 (from Table 26), against the work function,

The ability to ionically polymerize apparently correlates in many cases with the capacity of the substituents to act as electron acceptors (anionic polymerizability) or as electron donors (cationic polymerizability) on the rt-bond of the vinyl group. These relationships should be visible in carefully chosen quantum chemical parameters. 

Several doubts about the correctness of the usual statistical treatment were expressed already in the older literature (31), and later, attention was called to large experimental errors (142) in AH and AS and their mutual dependence (143-145). The possibility of an apparent correlation due only to experimental error also was recognized and discussed (1, 2, 4, 6, 115, 116, 119, 146). However, the full danger of an improper statistical treatment was shown only by this reviewer (147) and by Petersen (148). The first correct statistical treatment of a special case followed (149) and provoked a brisk discussion in which Malawski (150, 151), Leffler (152, 153), Palm (3, 154, 155) and others (156-161) took part. Recently, the necessary formulas for a statistical treatment in common cases have been derived (162-164). The heart of the problem lies not in experimental errors, but in the a priori dependence of the correlated quantities, AH and AS. It is to be stressed in advance that in most cases, the correct statistical treatment has not invalidated the existence of an approximate isokinetic relationship however, the slopes and especially the correlation coefficients reported previously are almost always wrong. 

Crude oils contain various amounts of indigenous surface-active agents that stabilize water-in-oil emulsions. Therefore crude oils may stabilize such emulsions. It has been shown that the effectiveness of a dispersant is dependent on both the dispersant type and the specific crude oil [309]. However, there is no apparent correlation between the degree of emulsion-forming tendency of the crude oil, which is a function of the indigenous surfactant content, and the effectiveness of the dispersant. In general, indigenous surfactants in crude oil reduce the effectiveness of the dispersant, but to an unpredictable level. 

It was shown later that a mass transfer rate sufficiently high to measure the rate constant of potassium transfer [reaction (10a)] under steady-state conditions can be obtained using nanometer-sized pipettes (r < 250 nm) [8a]. Assuming uniform accessibility of the ITIES, the standard rate constant (k°) and transfer coefficient (a) were found by fitting the experimental data to Eq. (7) (Fig. 8). (Alternatively, the kinetic parameters of the interfacial reaction can be evaluated by the three-point method, i.e., the half-wave potential, iii/2, and two quartile potentials, and ii3/4 [8a,27].) A number of voltam-mograms obtained at 5-250 nm pipettes yielded similar values of kinetic parameters, = 1.3 0.6 cm/s, and a = 0.4 0.1. Importantly, no apparent correlation was found between the measured rate constant and the pipette size. The mass transfer coefficient for a 10 nm-radius pipette is > 10 cm/s (assuming D = 10 cm /s). Thus the upper limit for the determinable heterogeneous rate constant is at least 50 cm/s. 

Similar observations have been reported by Pinto15 for the conformational equilibrium in 2-[(4-methoxyphenyl)seleno]-l,3-dithiane (Fig. 9). Although, at 273 and 300 K, the proportion of the more polar equatorial isomer 17 increases as the dielectric constant of the medium increases, no apparent correlation exists at low temperature. 

Even though Lp(a) and LDL are very similar in structural respects, there is no evidence that the biosynthesis or catabolism of Lp(a) and LDL are coupled, since there is no apparent correlation between the concentrations of Lp(a) and LDL in plasma (K36, K37, Sll). 

Ng, Tang and Sederholm 66> also reported the solvent dependence of 2/F F in the sp3 hybridized compound CF2BrCFBr2 (Table 28). Again, the coupling constant increases and there is an apparent correlation between solvent polarity and the magnitude of the change. 

In the case of alkenes, 1-pentene reactions were studied over a catalyst with FAU framework (Si/Al2 = 5, ultrastable Y zeoHte in H-form USHY) in order to establish the relation between acid strength and selectivity [25]. Both fresh and selectively poisoned catalysts were used for the reactivity studies and later characterized by ammonia temperature programmed desorption (TPD). It was determined that for alkene reactions, cracking and hydride transfer required the strongest acidity. Skeletal isomerization required moderate acidity, whereas double-bond isomerization required weak acidity. Also an apparent correlation was established between the molecular weight of the hard coke and the strength of the acid sites that led to coking. 

The bioassay technique was developed to reduce the uncertainties associated with the use of native vegetation or cultivated crops. Plants can be started under controlled conditions and exposed under standardized conditions. Species and cultivars can be selected for oxidant sensitivity and symptom characteristics. The two studies just noted were the most closely controlled. Similar work has not been repeated. However, many investigators have grown plants under known cultural conditions and then transplanted them to field sites where they received special care. These plants can then be read for foliar symptoms throughout a given period, and the symptoms related to oxidant concentrations. The lack of apparent correlation in the two early studies could be due to the lack of specificity for the monitored oxidants, the presence of different concentrations of interacting oxidants at different times, or variations in cultural conditions between exposure times. 

The mechanism in Fig. 14 applies equally well to both PVC and HPll. However, an unusual bond between the imidazole ring of His392 and the p-carbon of Tyr415 on the proximal side of the HPll heme has been identified (Fig. 13) (93), and subsequently its presence was correlated with heme oxidation. The apparent correlation between heme oxidation and His-Tyr bond formation suggested a mechanistic linkage between the two modifications and an alternate mechanism imique to HPll was proposed (Fig. 15). As with the first mechanism, the reaction assumes the formation of compound I that is available for reduction. Formation of the His-Tyr bond, involving a base catalyzed proton extraction from the... 

For theoreticians, such developments provide an opportunity to refine and test their more subtle inventions and to explain apparent correlations. I am quite sure they will seize this particular opportunity, given the exhavagant amount of data already accumulated, to choose amongst a crowd of competing models the one which best accounts for reality. 

King RB, Heine T, Corminboeuf C et al (2004) Antiaromaticity in bare deltahedral silicon clusters satisfying Wade s and Hirsch s mles an apparent correlation of antiaromaticity with high symmetry. J Am Chem Soc 126 430 31... 

The formation of the cross-linked products demonstrated an apparent correlation to H bonding sequences. What is the mechanism behind the observed sequence specificity One of two possible mechanisms, one kinetic and the other thermodynamic, may be involved in aqueous media. The kinetic mechanism involves intermolecular... 

It has been argued [235] by analogy with the case of molecules adsorbed on glassy n-hexane [232] that this enhancement is due to the electron transfer to CF2CI2 of an electron previously captured in a precursor state of the solvated electron in the water layer, which lies at and just below the vacuum level [300,301] and the subsequent. Similar results have been reported for HCl adsorbed on water ice [236]. It has been proposed that enhanced DEA to CF2CI2 via electron transfer from precursor-solvated states in ice [235] may explain an apparent correlation between cosmic ray activity (which would generate secondary LEE in ice crystals) and atmospheric ozone loss [11]. The same electron transfer mechanism may contribute to the marked enhancement in electron, and x-ray-induced dissociation for halo-uracil molecules is deposited inside water ice matrices [39]. 

---