This website is designed to assist the user in rapidly locating the relevant or desired content. The primary interface is a single search box located immediately underneath the depiction of a PAH molecule. When a user begins typing a PAH name, chemical formula, or CAS number into the search box, a list of matching compounds will appear immediately below. Note that the user must type at least three characters before possible matches appear. Selecting one of the names from the list by clicking or tapping on the name will cause the information on the selected molecule to be displayed in the space immediately below the search box.
The space in which results are displayed is organized into collapsible sections: Identifiers, Structure, Links, Spectra, Estimated Properties, and Thermochemistry. The data that appears in each section is described below. By default, on the Identifiers section will be open the user selects a compound. Other sections may be opened by clicking or tapping the title bar of the section (or the name or "+" icon in the title bar).
A selection of identifying information including
appears in this section.
This section contains two tabs that may be used to view a 2d or 3d depiction of the molecule.
In the 2d tab, a "stick structure" is displayed along with structural identifiers such as the SMILES notation, the International Chemical Identifier (InChI), and the InChIKey (a compact form of the InChI notation).
In the 3d tab, a rotatable 3d structure of the molecule is shown. The user may rotate the molecule by clicking and dragging within the molecule display area. This functionality is powered by JSmol which provides a great deal of additional functionality that is documented on their website. The structures that are displayed have been optimized at the B3LYP/cc-pVDZ level of theory.
Links are provided that permit download of
Links to several other sources of information on the compound of interest are provided. Note that in some cases these may not lead to a match.
In this section, three types of spectra are presented
The IR and UV/Vis spectra are displayed as "stick spectra" (red lines). The effect of spectral broadening is simulated by centering a Gaussian function on each "stick." The sum of these Gaussians is displayed in blue. The width of the Gaussian function is determined by the slider below the plot, and the value is displayed in a box at the left. The slider may be adjusted by clicking/tapping and dragging the slider to the desired broadening value. The broadened plot will adjust in real time as the slider is adjusted. Unchecking the "Plot stick spectrum" box will remove the disply of the stick spectrum from the plot. Similarly, unchecking the "Plot broadened spectrum" box will remove display of the broadened spectrum from the plot. Boxes may be checked/uncheck by clicking or tapping. The plot parameters may be reset to the default values by clicking or tapping the "Reset Plot" button at the bottom of the Spectra section. It is possible to zoom in on the plot area by selecting a range of frequencies/wavelengths. This is done by clicking and dragging in the plot area. This functionality may not work on mobile devices or devices with a touch interface.
NICS data are displayed using JMol, just like the 3d structure. In fact, a 3d depiction of the molecules with a number of additional small pink spheres is displayed. Clicking/tapping on or hovering over (mouse only) an atom or sphere will display the value of the magnetic shielding (ppm) at that point in space.
Four parameters which give information on the size of the molecule
are shown. This information is useful for predicting chromatographic retention times, and its use is more fully described in SP922 and elsewhere.
A number of properties derived from the quantum chemistry calculation (DFT) are displayed
The output from a transport property code (ZENO) is given. The user may download the output or scroll through it. Similarly, output from the US EPA EPI Suite is given.
In this section, a thermodynamic table in the style of the NIST-JANAF tables is given in the temperature range 0 - 5000 K. The enthalpy of formation data are computed from the results of an energy-extrapolated B3LYP/cc-pVDZ optimization and frequency calculation, and the remainder of the values are computed using statistical thermodynamics functions. All results are computed within the ideal gas, rigid rotor, harmonic oscillator approximation. For the enthalpy of formation data, an empirical correction based on a chemical group scheme is applied. For a complete description of how these data were derived, see "First Principles Prediction of Enthalpies of Formation for Polycyclic Aromatic Hydrocarbons and Derivatives," Thomas C. Allison and Donald R. Burgess Jr., manuscript in preparation. Additional information may be found in NIST Special Publication 1186: Thermodynamic Properties of Polycyclic Aromatic Hydrocarbons.
A menu appears in the upper left of the web site with links to information about the database (About), this help (Help), links to other web sites at NIST that may be of interest (Links), and credits for development of this web site (Credits). A set of indices (by name, formula, and CAS number) may be accessed from this menu as well.
The "X" button at the right of the search box will erase the contents of the search box when clicked.