PQRS regions

The conservative PQRS regions have very few substitutions (paired nucleotides are underlined, variable ones are in bold) the P region has none S has only one, in Rhynchostegium serrulatum ... 

The dotted curve PQR, separating the region of heterogeneous states from the regions of homogeneous states, is called the limiting curve of heterogeneous states, or the border curve. 

Now let us consider a system which exhibits two regions like QES. The portion of the phase diagram (at constant T and p) in the neighbourhood of these regions pqr and uvw will be like fig. 29.4. Now consider what happens when the temperature is changed at constant pressure. Suppose for example that as the temperature rises, the... 

At one point in this 1-ring buildup there are three possible isomers (Figure 2). The 7-ring dibenzo[e,ghi]perylene has three nonequivalent bay regions. A two-carbon addition to each of these will produce three different 8-ring PAHs. Two of these were previously known before this work,benzo[a]coronene and benzo[pqr]naphtho[8,l, 2-bcd]pery lene. The third was not, but a unknown compound was found which almost co eluted in the HPLC with benzo[a]coronene. This was isolated and shown to be the third isomer [5]. This can be taken as a tacit proof of the 1-ring buildup path. 

In the infrared region each vibrational transition is accompanied by a number of quantum transitions between rotational states of the molecules. In lower resolution spectra or if conditions for considerable broadening of absorption lines are present, the accompanying rotational transitions determine usually a non-symmetiic PQR stmctme of the infrared band. In higher resolution spectra the individual rotational lines are separated. The intensity of an infrared absorption band represents, therefore, a sum over the intensities of all fine structure lines associated widi the respective vibrational transition. It is, thus, necessary to describe the factors determining intensities of die component rotational lines and, then, see how these sum up into overall intensity of an infrared band. 

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