A Semantic blog is one in which the system at least in part understands about (some of the) concepts and topics that are in the content. The idea is that this content can be more intelligently (is that the correct word?) and importantly, automatically searched, harvested, and connected to the same or similar concepts found elsewhere in other blogs and the Web as whole. I am writing this blog using Firefox, having added a Firefox extension called Zemanta. As I write, the system offers suggestions for similar themes elsewhere that I could choose to link to the blog (and obviously the more one writes, or the more specific the terms one uses, the more sensible the suggestions become. At this precise moment, it is still offering fairly generic suggestions, one of which I have just chosen to add). My purpose in this particular post is to explore how the very process of writing a blog might be affected by such a product. I am also inferring (but cannot add detail at the moment) that all the (semantic) connections or links to other materials will be expressed in this blog using some form of formal declaration, such as e.g. RDF or RDFa.
Semantic Blogs
January 17th, 2010Chemical intimacy: Ion pairs in carbocations
January 11th, 2010The scheme below illustrates one of the iconic reactions in organic chemistry. It is a modern representation of Meerwein’s famous experiment from which he inferred a carbocation intermediate, deduced from studying the rate of enantiomerization of isobornyl chloride when treated with the Lewis acid SnCl4.
How long will a blog last? ArchivePress
January 9th, 2010After around 40 posts here, I decided to take a look at the whole effort and ask some questions. For example
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Contriving aromaticity from S≡C Triple bonds
January 1st, 2010In the previous post, the molecule F3S-C≡SF3 was found to exhibit a valence bond isomerism, one of the S-C bonds being single, the other triple, and with a large barrier (~31 kcal/mol, ν 284i cm-1) to interconversion of the two valence-bond forms. So an interesting extension of this phenomenon is shown below:
Clar islands in a π Cloud
December 9th, 2009Clar islands are found not so much in an ocean, but in a type of molecule known as polycyclic aromatic hydrocarbons (PAH). One member of this class, graphene, is attracting a lot of attention recently as a potential material for use in computer chips. Clar coined the term in 1972 to explain the properties of PAHs, and the background is covered in a recent article by Fowler and co-workers (DOI: 10.1039/b604769f). The concept is illustrated by the following hydrocarbon:
The nature of the C≡S triple bond: part 3.
December 6th, 2009In the previous two posts, a strategy for tuning the nature of the CS bond in the molecule HO-S≡C-H was developed, based largely on the lone pair of electrons identified on the carbon atom. By replacing the HO group by one with greater σ-electron withdrawing propensity, the stereo-electronic effect between the O-S bond and the carbon lone pair was enhanced, and in the process, the SC bond was strengthened. It is time to do a control experiment in the other direction. Now, the HO-S group is replaced by a H2B-S group. The B-S bond, boron being very much less electronegative than oxygen, should be a very poor σ-acceptor. In addition, whereas oxygen was a π-electron donor (acting to strengthen the S=C region), boron is a π-acceptor, and will also act in the opposite direction. So now, this group should serve to weaken the S-C bond.
The nature of the C≡S Triple bond: Part 2
December 5th, 2009In my first post on this theme, an ELF (Electron localization function) analysis of the bonding in the molecule HO-S≡C-H (DOI: 10.1002/anie.200903969) was presented. This analysis identified a lone pair of electrons localized on the carbon (integrating in fact to almost exactly 2.0) in addition to electrons in the CC region. This picture seems to indicate that the triple bond splits into two well defined regions of electron density (synaptic basins). In a comment to this post, I also pointed out that an NBO analysis showed a large interaction energy between the carbon lone pair and the S-O σ* orbital, characteristic of anomeric effects (in eg sugars). This latter observation gives us a handle on possibly tweaking the effect. Thus if the S-O σ* orbital can be made a better electron acceptor, then its interaction with the lone pair could be enhanced.
The nature of the C≡S triple bond
December 1st, 2009Steve Bachrach has just blogged on a recent article (DOI: 10.1002/anie.200903969) claiming the isolation of a compound with a C≡S triple bond;