Studies in the synthesis of pure hydrocarbons

Research into the synthesis of pure hydrocarbons received much stimulus during the war years, when the characteristics of as large a number of pure hydrocarbons as possible were needed. The present study formed part of a wide scheme for this purpose. During the work on synthesising hydrocarbons the author found that, inasmuch as the synthesis of pure hydrocarbons depended to a large extent on the Grignard reaction, it was necessary to try to obtain a better understanding of this reaction. This Thesis therefore serves two purposes. It describes the author's investigation of the abnormal reaction of Grignard reagents with carbonyl compounds, and it describes the synthesis of two hydrocarbons, 2:4: 6-trimethylheptane and 2:3:5-trimethylhexane, and the preparation of four others, believed to be new:3:4-dimethylnonane, 3:4-dimethyloctane, 2;4:5-trimethylheptane, 2:6-dimethyl-4-isobutylheptaneThe investigation of the Grignard reaction occupies the larger part of the thesis, and is devoted to a survey on some of the past work on abnormal Grignard reactions, to a discussion of the mechanisms of abnormal reactions, and the application of the author's results to these mechanisms. The author's results lead him to refute the "alcoholate" and "addition" mechanisms, and to postulate that all Grignard reagents can dissociate homolytically and heterolytically, the extent to which any Grignard reagent does so depending on the nature of the Grignard reagent and the nature of the second reactant. The author concludes that, for this reason, the mechanism of reduction of carbonyl compounds by Grignard reagents is one of free radicals, whereas that of enolisation and condensation is ionic.<p

A Tale Of Two Spicules: The Impact of Spicules on the Magnetic Chromosphere

We use high-resolution observations of the Sun in Ca II H 3968 A from the Solar Optical Telescope on Hinode to show that there are at least two types of spicules that dominate the structure of the magnetic solar chromosphere. Both types are tied to the relentless magnetoconvective driving in the photosphere, but have very different dynamic properties. ``Type-I'' spicules are driven by shock waves that form when global oscillations and convective flows leak into the upper atmosphere along magnetic field lines on 3-7 minute timescales. ``Type-II'' spicules are much more dynamic: they form rapidly (in ~10s), are very thin (<200km wide), have lifetimes of 10-150s (at any one height) and seem to be rapidly heated to (at least) transition region temperatures, sending material through the chromosphere at speeds of order 50-150 km/s. The properties of Type II spicules suggest a formation process that is a consequence of magnetic reconnection, typically in the vicinity of magnetic flux concentrations in plage and network. Both types of spicules are observed to carry Alfven waves with significant amplitudes of order 20 km/s.Comment: 8 pages, 5 figures, accepted for Hinode special issue of PAS

Reversal-free CaIIH profiles: a challenge for solar chromosphere modeling in quiet inter-network

We study chromospheric emission to understand the temperature stratification in the solar chromosphere. We observed the intensity profile of the CaIIH line in a quiet Sun region close to the disk center at the German Vacuum Tower Telescope. We analyze over 10^5 line profiles from inter-network regions. For comparison with the observed profiles, we synthesize spectra for a variety of model atmospheres with a non local thermodynamic equilibrium (NLTE) radiative transfer code. A fraction of about 25% of the observed CaIIH line profiles do not show a measurable emission peak in H_{2v} and H_{2r} wavelength bands (reversal-free). All of the chosen model atmospheres with a temperature rise fail to reproduce such profiles. On the other hand, the synthetic calcium profile of a model atmosphere that has a monotonic decline of the temperature with height shows a reversal-free profile that has much lower intensities than any observed line profile. The observed reversal-free profiles indicate the existence of cool patches in the interior of chromospheric network cells, at least for short time intervals. Our finding is not only in conflict with a full-time hot chromosphere, but also with a very cool chromosphere as found in some dynamic simulations.Comment: 8 pages, accepted in A&

Chromospheric Anemone Jets as Evidence of Ubiquitous Reconnection

The heating of the solar chromosphere and corona is a long-standing puzzle in solar physics. Hinode observations show the ubiquitous presence of chromospheric anemone jets outside sunspots in active regions. They are typically 3 to 7 arc seconds = 2000 to 5000 kilometers long and 0.2 to 0.4 arc second = 150 to 300 kilometers wide, and their velocity is 10 to 20 kilometers per second. These small jets have an inverted Y-shape, similar to the shape of x-ray anemone jets in the corona. These features imply that magnetic reconnection similar to that in the corona is occurring at a much smaller spatial scale throughout the chromosphere and suggest that the heating of the solar chromosphere and corona may be related to small-scale ubiquitous reconnection.Comment: 10 pages, 5 figure