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There has been concern for many years that phosphorus (P) from engine oils is volatilised, passes through the combustion chamber and is deposited on the catalyst system in passenger cars, causing the emission control system to lose efficiency. Therefore, as new engine oil specifications have been introduced, there has been a trend to require a reduction in P in fresh engine oils. The primary P source in current engine oils is zinc dithiophosphate (ZDP), which acts as an anti‐wear agent and antioxidant. Therefore, a reduction in P in the oil could compromise the anti‐wear and antioxidant performance of engine oils. Another detrimental effect of ZDP is that it is known to increase friction in the mixed lubrication regime, which in turn would decrease the ability of engine oils to improve fuel economy. Metal‐free P‐containing anti‐wear additives (MFPAWs) have been used for many years in other automotive and industrial lubricants. We examined the effect of an MFPAW in catalyst efficiency and fuel economy engine tests. Catalyst protection and the fuel economy benefits of engine oils were improved when the MFPAW was used in place of ZDP. Therefore, the total P content of an engine oil does not need to be reduced if the proper anti‐wear additive is selected. Copyright © 2007 John Wiley & Sons, Ltd.

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The "N chemical shifts of a number of polyazaindenes have been determined, and have been correlated with the degree of contribution to the ground state of those resonance structures which place a partial positive charge on the bridge-bead nitrogen.The study of the chemistry and spectroscopic properties of polyazaindenes have interested us for some time.' A recent publication2 has described the results of some I4N NMR studies of pyrrocolines with additional nitrogens in the 5-membered ring ( We have now obtained the 15N spectra of a number of imidazo[ 1,2-a]pyridines with additional nitrogens in the 6-membered ring C, and have re-examined, by means of 15N spectroscopy, some of the compounds already described by Stefaniak.2 It is the purpose of this report to interrelate these results and to correlate the "N chemical shifts with respect to the major resonance contributing structures A and B, respectively. These resonance contributing structures were suggested on ' H NMR and chemical reactivity grounds some time ago.' A B Table 1 gives the 15N chemical shifts obtained in this study, as well as those reported in Ref. 2. Among all of these compounds N-4, the bridge-atom, is always the most shielded nitrogen, except in some instances where it is directly bonded to another nitrogen atom (8, 9, 11). The contribution of resonance structures such as A or B clearly places a partial positive charge on the bridge nitrogen and a partial negative charge on N-1 or N-2, respectively.* Author to whom correspondence should be addressed. the 'sole' resonance contributing structure to the ground state, the N-4 chemical shift would be similar to that of I5N in N-alkylpyridinium ions (this, of course, is only a qualitative comparison). Conversely, the more deshielded a particular N-4 with respect to other polyazaindenes, the less this resonance structure