Chem 125 Lecture 79/20/06

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Exam 1 - Friday, Sept. 29 !

Covers Lectures through next Wednesday

Including:

Functional GroupsX-Ray Diffraction

1-Dimensional Quantum Mechanics(Sections I-IV of webpage

& Erwin Meets Goldilocks)

Get-aquainted session Friday afternoon 4-5:30 in 160 SCL

TAsGözde

Josh

BrianDavid

All in WLH 114

7-9Tuesday

8-10Sunday

7-9Thursday

In 1895 RöntgenDiscovers X-Rays

Shadow ofFrau Röntgen'sHand (1895)

In 1912 LaueInventsX-Ray

DiffractionCuSO4 Diffraction

(1912)

Wm. Lawrence Bragg(1890-1971)

Determined structure of ZnS from Laue'sX-ray diffraction

pattern (1912)

Youngest Nobel Laureate(1915)

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Tungsten Interconnect in Computer Chip

Nanotomography Comes of Age, Nature, August 10, 2006

“They then use tomographic methods to combine images taken at different incident X-ray angles, allowing internal structures and - given sufficent spectral resolution - chemical bondings to be discerned with a spatial resolution of around 60 nanometers.”

"Seeing" IndividualMolecules, Atoms, Bonds

Collectivelyby X-Ray Crystallography

Blurring Problem

Blurring Problem from Motion and Defects

Time Averaging

Space Averaging in Diffraction(Cooperative Scattering)

Advantage for SPM(Operates in Real Space)

What can X-ray diffraction show?

How does diffraction work?

Like all light, X-rays are waves.

Atoms?Molecules? Bonds?

Interference of Ripples

WaveMachines

Bragg Machinehttp://www.eserc.stonybrook.edu/ProjectJava/Bragg/

Breaks?

Real Space "Reciprocal" Space

Material Diffraction Photo

Molecular Structure Fuzzy Pattern

Crystal Lattice Viewing Holes

Decreasing Spacing Increasing Spacing

Direct

Two Scattering Directions are Always Exactly in Phase

“scattering vector”

Specular perpendicular to scattering vector

All electrons on a planeperpendicular to

the scattering vectorscatter in-phase at

the specular angle !

Specular

Simplification from Electrons-on-a-Plane Trick

scattering vector

3 24 1

scattering vector

10

Simplification from Electrons-on-a-Plane Trick

3

+2

+4

+1

12

3

Net in-phasescattering

TotalElectrons

3 24 1

Water

Oil“Thickness” ~ 200 nm

Path Difference = 400 nm

= 0.5

Strong400 nm

Scattering

No800 nm

Scattering

= 1

scattering vector

scattering vector

Simplification from Electrons-on-a-Plane Trick

10

3

+2

+4

+1

Net in-phasescattering

TotalElectrons

12

3

Suppose first path difference is half a wavelength.(increase or decrease angle)

3

+2

-4

-1

0

0.51

1.5

3 24 1

Benzene Snowflake

Slide with Random

(but Oriented)"Benzenes"

Benzene Snowflake

Isolated“Benzenes”

Benzene Snowflake

1

√3√3

[1]Reciprocal

Isolated“Benzenes”

Closely-spacedplanes give

high angles.

Benzene Snowflake

Isolated“Benzenes”

2D Latticeof

“Benzenes”

Filament

Light BulbFilament(helix)

Filament

Light BulbFilament(helix)

X angle tellshelix pitch

Spot spacingtells scale

Spot spacingtells scale

Spots weakensuccessively

(from wirethickness)

(given &

screen dist)

HELIXw

S

Svw

SCuriousIntensitySequence

B-DNAR. Franklin

(1952)

EvenDouble Helix

Wouldcancel"Odd #

reflections"

wS

Svw

SCuriousIntensitySequence

B-DNAR. Franklin

(1952)

OffsetDouble Helix

BASE STACKING

B-DNAR. Franklin

(1952)

wS

Svw

S

MAJOR& MINORGROOVES

HELIX DIAMETER

End