x ray Flashcards
(12 cards)
4 thinsg xray tell you
– where atoms are (you can actually ‘see’ them!)
– how they are connected to form molecules
– how they pack to form crystals
– to what extent they are vibrating
3 things you need to knwo to describe a crytsal
Unit cell type and dimensions
3 angle (alpha, beta, gamma) and lengths (a, b, c)
Atomic coordinates
0 is origin and 1 is end, value in-between tells us where it is relative to unit cell axes
Space group symmetry
molecules are related by symmetry elements
how to tell if orthorhombic and monoclinic
orthorhombic
all sides not equal
all angles are 90
monoclinic
not all sides equal
alpha and gamma are 90 but beta is not
Z and Z’ MEANING
Z = Total number of molecules in the unit cell
Z’ = the number of unique molecules in the unit cell
do we need to know eevry molecules space
we need to find just ONE molecule, and as long as we know the symmetry relationships between the molecules, we automatically know where the others are
x-ray strength and electrons
Atoms with lots of electrons scatter strongly (e.g. Au) and so can be ‘seen’ easily
Atoms with few electrons (e.g. H) scatter weakly and so are much more difficult to ‘see’
braggs law
wavelength equal to 2x spacing butene interplanar space X sin angle of diffraction
what can you use braggs law for and what do you need to find out
if measure angle of diffraction then you can work our interplanar space using equations
what does it mean if there is a center of symmetry
then it must be racemic, as the mirror or centre relates the left handed molecules to the right handed ones
2 reasons why use powder
Generally, used when you can’t grow a single crystal of the API of interest
Or when dealing with bulk powders in pharmaceutical industry
what is amorphous hump
fuzzy short-range line
3 ways you can see a polymorph
Change apparent in patterns (peak positions different,
peak heights different), because the crystal structure
(unit cell and atom positions) has changed
