Software
Drawing Structures and 13 Calculating C NMR Spectra
ACD/CNMR Advanced Chemistry Development 141 Adelaide St. West, Ste. 1501 Toronto M5H 3L5, Canada 416-368-3435; fax 416-368-5596; info® acdlabs.com; http://www.acdlabs. com Version 1.1; $1499; $$125 5overnment; $799 academic
Comparison of chemical shifts with those of known compounds and 13C chemical shift estimation are perhaps the two most widely used approaches in the assignment of 13C NMR spectra. Spectral collections are very useful in the first approach, and some vendors offer computer-assisted search programs. The second approach, based on the additivity of substituent effects on 13C NMR chemical shifts, has proven useful in interpreting 13C NMR spectra. Although these methods provide reasonably accurate estimates of 13C chemical shifts they are cumbersome and complicated with extensive tables of correction. Also they do not work well with heterocyclic compounds or with highly substituted carbons ACD/CNMR ii s Windows-based 13C NMR simulation program that uses a database of 13C chemical shifts to predict the 13 C NMR spectrum. It requires a PC with h 386 or higher processor, a math coprocessor, a 3.5-in. high-density floppy-disk drive, 4 MB of RAM, and 11 MB of free eard-disk space. Although the manual indicates that ACD/CNMR works undee Windows s5,1 installed it under Windows 3.1 only. 740 A
Installation of ACD/CNMR is similar to that of other Windows-based products. The software is protected to the extent that it checks for the user registration number assigned for each copy. A click on the ACD/CNMR icon opens the ACD/CNMR window, which is equipped with toolbars and a pop-up explanation of each tool button. A click on the "Molecule" button at the bottom of the screen takes you to the Molecule Editor window. Drawing structures with this editor is quite simple and intuitive. Structures are drawn with the mouse the way they appear on paper. One click on a single bond produces a double bond, two clicks produces a triple bond, and another click on the bond returns it to a single bond. Changing atoms is also very convenient. Clicking on the atom icon activates the atom, which remains active until it is
changed by clicking on another atom. The "Clean" option in the View menu converts the original structure to one with the correct bond lengths and angles. Unlike some of the other drawing programs I've used, ACD/CNMR retains the cis configuration of an original uncleaned structure. The program also displays and tracks the elemental composition and molecular formula of the structure as it is drawn. Although the editor lacks some of the sophisticated editing features found with dedicated drawing programs, the lack of those features has no noticeable effect on the efficiency and ease of use of the program. Structures can be exported or imported into .MOL files conveniently and effortlessly, and all imported and exported structures retain their chemical significance. Once the structure is drawn, a click on the CNMR Spectrum button begins the
ACD/CNMR uses a database of 13C chemical shifts to predict the 13C NMR spectrum of a user-drawn chemical structure.
Analytical Chemistry News & &eatures, December 1, 1996
CNMR calculations. The calculated spectrum is displayed with the structure in an inset window that can be moved and resized. The Subwindows menu allows you to add the peak listing of the spectrum in a table. This display can be placed on a report page for further editing and printing of the structure, peak table, and spectrum. The report editor allows changing of fonts, size, and automatic numbering of the atoms. Although the program normally uses its internal chemical shift database, a user-generated database can be used with the internal database to improve the accuracy of chemical shift prediction. Although calculated shifts are usually accurate to ±5 ppm, larger variations are not uncommon. ACD/CNMR can nb particularly useful in the assignment of quaternary carbon atoms, which can be tricky, especially when they are removed from nearby protons. For example, the 13C NMR spectrum of dinitrile in DMSO-d6 at room temperature shows only five quaternary peaks instead of six. Proton NMR and mass spectral data together with the elemental analysis were consistent with the structure, and all attempts to locate the missing quaternary carbon in the aromattc region were unsuccessful. When ACD/CNMR waa ssed to simulate the 13C NMR spectrum, the predicted spectrum showed the C-8 quaternary carbon at 47.9 ppm, unusually far upfield. Surprisingly, the actual spectrum in DMSO-d6 shows a weak quaternary peak at 41.5 ppm, but t Iad presumed it to be related to an impurity and therefore ignored it Later, a quantitative spectrum obtained on the dinitrile confirmed the assignment of that carbon. The program is also useful for elucidating possible tautomers for a given structure. To the experienced organic chemist, this feature may appear trivial, but it can sometimes provide needed clues about a structure.
I was initially reluctant to use a simulaData Pro tion program because of fhe inertia of fearn- Renaissance Software ing (and mastering) a new molecular ediP.O. Box 17 tor. However, the usefulness of ACD/ Dresher, PA 19025 CNMR soon had me convinced oo its stility. 215-619-0130; fax 215-619-0131 ACD/CNMR proviide fairly aacurate ehem- $950 ical shifts most of thetime,although the current version lacks the ability to display Data Pro ccntains the American IIstitute the structures or structural fragments used of Chemical Engineers' DIPPR Pure Comin predicting the chemical shifts. It should ponent Physical Property Database with a prove invaluable to spectroscopists or Windows interface. Users can perform chemists engaged in interpretation of 13C combination searches on any part of a NMR for structure elucidation. chemical's name, synonym, formula, or Reviewed by Sadanand V. Pathre, 3Mstructure, or on the CAS number. A multiproperty search option allows the user to Company, St. Paul, MN search for compounds with the properties required for a specific application or to identify unknown compounds. System SOFTWARE RELEASED requirements include an IBM-compatible computer with a 386 or higher processor ChromKeeper 4 MB RAM 12 MB available hard-disk Softshell space and a VGA monitor. 1600 Ute Ave. Grand Junction, CO 81501 970-242-7502; fax 800-242-6469;
[email protected]; http://www.soffshelll com $99
ChromKeeper allows users to insert chromatographic data into word processors, spreadsheets, and database files as OLE objects. The chromatograms can then be edited inside reports, presentations, or articles using tools that are designed for working with the data. Chromatograms can be saved in standard ANDI or netCDF format ChromKeeper is designed to function as as OLE server application and can only be started from inside an OLE-compatible application, such as Microsoft Word. It alloww the user to zoom in and display any part of the graph. Minor editing of the appearance of the curves is possible including changes to headers footers colors and size System requirements include Windows 95 or NT running on a PC wiih a 486 oo highee processor and 12 MB RAM
SiteSTAT Pioneer Systems Development 12902 N.E. 91st Lane Kirkland, WA 98033-5967 206-822-4461; fax 206-822-4637;
[email protected] Version 1.0; $495
SiteSTATis a virtual data analysis tool for managing, evaluating, and reporting environmental analytical data. Data can be imported from a variety of file formats, including Lotus 123, Excel, Paradox, dBASE, and ASCII, and all data from a site can be stored in one project database. Features include data qualifier weighting factors, unit conversion factors, context-sensitive help, and an online tutorial. System requirements include a PC running Windows 3.1 or Windows 95, a 386 oo highee processor and 4 MB RAM. Microsoft NT server and NetBIOS-compatible networks such as Novell and Lantastic supported.
Analytical Chemistry News & Features, December 1, 1996 741 A
