all elements present in the metallic medicne may be unknown. What would be the process of determining the molecular formula using XRD( X-Ray Diffraction)
2007-07-14 06:19:56 · 4 answers · asked by Ann 1 in Science & Mathematics ➔ Chemistry
Ann,
XRD can only be used for structural analysis... in other words, it is used to find the arrangement of atoms in a crystal once something about the composition of the compound is already known. So no, it cannot be used to determine the molecular formula.
Before solving the structure with XRD, you need to use a technique that will tell you what elements are present in this medicine. An elemental analyzer (EA), X-ray fluorescence (XRF), atomic emission spectroscopy (ICP-AE), or mass spectroscopy (ICP-MS) will all serve this purpose. Which one you use will depend on how large a sample of the medicine you have, and what elements you believe to be present in it. You should consult an analytical chemist at wherever you are doing your work, and they can help you decide what technique would be best suited for your problem.
Afterward this, you can use XRD (if the medicine can be crystallized), or IR spectroscopy to find information about the structure of the molecule.
Ann,
Depending on how complex your molecule is and whether it contains metal atoms that are significantly heavier than the organic constituents of the medicine you are studying, "Fly on the Wall's" addendum may very well be correct. It is certainly possible to solve a crystal structure without any prior knowledge of the composition, but it takes a detailed knowledge of single crystal methods. I would still recommend doing some sort of elemental analysis so that you have a rough idea of the composition before you proceed with XRD, but "Fly on the Wall" is correct that my expertise is in inorganic structures, and you may be able to get a good solution with XRD alone. Fly on the Wall... I admire your commitment to checking back on questions and giving the most accurate information you can!
2007-07-14 06:37:14 · answer #1 · answered by mnrlboy 5 · 0⤊ 0⤋
i agree with the fly on the wall-as long as it is organic, and you have it as a single crystal-a structure determination is possible, even if you have no idea what´s in there. the accuracy might be lower, but a good prediction is still possible. (i´ve actually misused our XRD operator in this way a few times myself).
but if you just need the molecular formula, why waste time/money on a X-ray (where u get lots more info, that u don´t need) and not just use MS and EA.
Respect for mnrlboy, not many here admit to not being always right!
2007-07-14 20:28:51 · answer #2 · answered by chem_freak 5 · 0⤊ 0⤋
Presuming the substance is a single-crystalline solid (for example a molecular substance containing one or more metal atoms often is crystalline) then yes X-ray diffraction would be able to determine the composition and molecular structure.
I beg to differ with the next answer. You CAN determine the composition of a molecular substance by X-ray crystallography. The process of solving the structure is a series of successive approximations. Once one atom is located (especially a metal atom) others around it can be located and identified by their X-ray scattering intensities. Of course the process is much faster if you have an idea of the composition already -- but you only need to be close. The next answer was submitted by someone familiar with geological X-ray diffraction, and in the case of minerals this might actually be very difficult or impossible, but with organic compounds it is possible.
2007-07-14 06:31:09 · answer #3 · answered by Fly On The Wall 7 · 0⤊ 0⤋
Molecular configuration, not formula.
2007-07-14 06:48:34 · answer #4 · answered by ag_iitkgp 7 · 0⤊ 1⤋