Feb 7

Question 1

What does Patterson Function do?>

Answer 1

It is based on electron density as get peaks of intensity at atom locations. This function gives peaks for interatomic vectors. So move each atom to the origin 1 at a time, then draw the positions to other atoms. The peak at origin is from self vector (atom with itself)

Question 2

How to locate heavy atoms from Patterson Function?

Answer 2

You get the plot, then draw a vector between any 2 points. Put that same vector starting from the origin, if it ends up at an atom, then that is a possible heavy atom

Question 3

How does space group symmetry help us find heavy atoms?

Answer 3

If you know what the equivalent positions at other coordinates other than x,y,z like -x, y+1/2, -z. We then know we should be looking for peaks in these spots

Question 4

What is the Harker plane?

Answer 4

It is when interatomic vector v=1/2, it is betwwen symmetry related atoms?

Question 5

Enantiomer problem and patterson map?

Answer 5

Patteron map has center of inversion, so both the correct and enantiomer of the molecule will be solutions. You might need to use other if you get iffy data.

Question 6

What is anomalous scattering?

Answer 6

It is when heavy atoms absorb x-rays of certain wavelengths, so Friedel law not hold,the intensity of hkl reflecction will be different from -h,-k,-l relfection. Normally these intensities are the same, but the structure factor is not as they are diff phases

Question 7

What get from minimum and maximum of the peaks f’ and f’’ respectively?

Answer 7

f’ minimum peak will give same xray energy value as inflection point of f’’, and inflection point will give same value as max peak of f’’. You want to collect data at these values to locate heavy atoms