Daniel R. Mills

Magnetic resonance of intercalation compounds of graphite: Questions of ionicity and mobility of inserted species

Abstract Graphite will react at room temperature with Lewis acids as PF 5 and BF 3 in the presence of the oxidant C1F to form intercalation compounds containing closed-shell anions. In the case of “C 16 BF 4 ”, the chemical shifts of both 11 B and 19 F nuclear magnetic resonances point to the existence of BF − 4 , rather than the initial BF 3 , within the graphite planes. The existence of second order quadrupolar coupling of the 11 B resonance suggests, however, possible hybrid BF 3 BF − 4 character, as in B 2 F − 7 , a known dimeric anion of BF 4 and BF 3 . NMR results on 19 F and 31 P in the two compounds “C 14 PF 6 ” and “C 28 PF 6 ” support this hypothesis, as “C 28 PF 6 ” shows only the presence of PF − 6 , but the more concentrated “C 14 PF 6 ” shows composite PF 5 PF − 6 character. Our claim for intercalated anions in these systems is reinforced both by radical cation-type signals in the ESR and by deshielding effects in the 13 C NMR. The narrow linewidths of the nuclear magnetic resonance absorptions of the intercalated species are suggestive of “liquid-like” behavior.

The interaction of potassium with graphite and other benzenoid systems

Abstract Potassium can reduce benzenoid systems ranging from graphite to bituminous coals. We have examined the nature of this reduction by electron spin resonance of “C 8 K” products formed by heating potassium metal directly with SP-1 graphite, 13 C-labelled “amorphous carbon”, and Spherocarb. Graphite C 8 K possesses a linewidth linearly proportional to temperature, as is the case for sodium metal, and in contrast to the behavior of graphite/acceptor compounds. The other C 8 K compounds show both a narrow and a broad resonance, reflecting respectively benzenoid anions and dispersed potassium metal. In contrast, Illinois #6 coal, when reduced by potassium naphthalenide in tetrahydrofuran at 23°C, shows only slight changes in the ESR spectrum.

X-RAY DIFFRACTION OF N-PARAFFINS AND STACKED AROMATIC MOLECULES: INSIGHTS INTO THE STRUCTURE OF PETROLEUM ASPHALTENES

ABSTRACT X-ray diffraction investigation of normal paraffins and Debye internal interference calculations on stacks of aromatic molecules are used to make inferences about the structure of petroleum asphaltenes. The gamma band, a broad peak near 4.5 A, is associated with weakly ordered paraffins. Stacks of aromatic molecules can give rise to diffraction peaks at d value higher than that of the “(002)” line. X-ray diffraction of the liquids n-hexadecane, decalin, perhydro-fluorene, 1,3 dimethyladamantane, and 1-methyl naphthalene confirms the above insights and demonstrates that diffraction can distinguish among the organic structural types “paraffinic,” “naphthenic,” and “aromatic.”

More on the reaction of graphite/potassium with water

Abstract The first stage intercalation compound of graphite with K°, C 8 K, will react with water at room temperature to yield a solid product containing graphite inserted with potassium cations and water molecules. Temperature-variant 1 H NMR shows that both T 1 and T 2 decrease as temperature decreases from 298 K to 213 K (T 1 > T 2 at these temperatures) with an activation energy of 0.25 eV. Starting with a C 8 K D 2 O product, one can isotopically exchange with H 2 O to yield a product with 17% H 2 O after 48 hours at room temperature, showing the inserted species are not kinetically “encapsulated.” X-ray diffraction, thermogravimetric analysis, and nuclear magnetic resonance are used to distinguish the graphite compound from a mixture of graphite and hydrates of potassium hydroxide.

121Sb nuclear magnetic resonance of a GraphiteSbCl5 intercalation compound

Graphite will react at room temperature with SbCl5 to form a second stage, orthorhombic, intercalation compound of lattice parameters a0 = 849 pm, b0 = 738 pm, and c0 = 1272 pm. 121Sb nuclear magnetic resonance (15 MHz, 23°C) in the dispersive mode reveals a signal of width 7100 Hz located at 384 ppm downfield from SbCl−6. Electron spin resonance (9.5 GHz, 23°C) shows an asymmetric, ca. 95 G wide line of Dysonian center at g = (2.0024±0.0014). These results are consistent with oxidative intercalation of graphite by SbCl5 to form a compound containing both SbCl−6 and SbCl5. Our findings are compared to work on the analogous intercalate C10AsF5 and on the “overoxidized” material formed by reaction of graphite with WF6 and F2.

Still more on the reaction of the intercalation compound C8K with water

Abstract The reaction of C 8 K made from polycrystalline Ultracarbon with D 2 O leads to a solid phase product containing both potassium and water. The absence of quadrupole splitting in the 2 D NMR of the product argues against the presence of crystalline water of hydration, as in potassium hydroxide monohydrate. X-ray diffraction and electron spin resonance show the carbon skeleton to be inequivalent to the initial graphite. Hydrogen evolution in the reductive protonation of the dianion of perylene is shown to arise from an unstable intermediate hydroaromatic species.

The Chemistry of Internal Combustion Engine Deposits — II. Extraction, Mass Spectroscopy and Nuclear Magnetic Resonance

The minimum fuel octane required to avoid knocking in an internal combustion engine is not constant, but rather increases as the engine runs. This phenomenon, termed octane requirement increase (ORI), has long been recognized as being attributable to combustion chamber deposits.1 In spite of many excellent studies which describe the mechanisms by which combustion chamber deposits cause ORI1–5 and the impact of fuel and lube properties on the magnitude of ORI1,5–11 little is known about the nature of the deposit.1,10,11,13 With an understanding of the deposit structure, the chemistry involved in its formation should be more evident. Manipulation of this chemistry could reduce or modify these deposits and thereby achieve the goal of minimizing the octane required for satisfactory engine performance. The initial phase of our work, the characterization of deposit structure, is reported here.

The Chemistry of Internal Combustion Engine Deposits — I. Microanalysis, Thermogravimetric Analysis, and Infrared Spectroscopy

As an automobile engine runs, its fuel quality requirements, as measured by the octane number of the fuel needed to inhibit knocking, may change in time. Historically, this phenomenon is referred to as the “ORI”, standing for octane requirement increase.