Chem 345: Please Read Three Handouts White Problem Set Yellow Syllabus It won’t be graded, so it is not due. Answer key will be posted on canvas. Yellow Syllabus Read this. Pay close attention to exam dates/times for conflicts. I am serious about the academic misconduct policy. All of the information about the grading scale is present. Ivory Powerpoint Slides We will be going over these the first three days of lecture. Be sure to bring them for the first few days.

Why I will lie to you: What students think the answers should be: The Reality: Overgeneralizations allow this type of environment: At the next level, some of the overgeneralizations are removed:

Seeing molecules with a different set of eyes Chem 345 Spectroscopy Seeing molecules with a different set of eyes

Basis of Spectroscopy Higher Energy Empty State ENERGY In ENERGY Out Some Energy is Absorbed Low Energy Filled State Detector Ground State Excited State

Types of Spectroscopy UV-Vis: Electronic transitions Highly conjugated systems Eyes, analytical colormetric tests, Beer’s Law Infrared: Bond stretching Functional group determination C=O ~1700 cm-1 C N ~2200 cm-1 O-H, N-H ~ 3300 cm-1 Microwave: Molecular rotation Microwave ovens Interstellar molecules (McMahon Research Group)

Types of Spectroscopy Nuclear Magnetic Resonance (Radio Frequency) Nuclear Spin 1H (better known as proton) and 13C most widely used 2H, 6Li, 14N, 15N, 31P, 19F, 29Si are also possibilities 1H is the common isotope of hydrogen (>99%) 13C is not very abundant (~1% of carbon) Differences in natural abundance between carbon and hydrogen lead to subtle differences in NMR capability Large magnetic fields generate the different energy states

900 MHz NMR Spectrometer 21.1 Tesla (~ 107 times higher than Earth’s magnetic field) ~ 95 miles of superconducting wire inside

Crude NMR Description DE~ Radiowave 700 100 200 600 DE~ Radiowave 400 400 900 MHz instrument at NIH site = approx 20 T Its got its own spiral staircase!! Higher magnetic field = greater sep between +1/2 & -1/2 states = more sensitive INCREASING MAGNETIC FIELD 8

3 Characteristics of NMR Spectra Chemical Shift (Carbon and Proton) Type of carbon/protons Number of inequivalent protons/carbon Clues about their local environment Integration (typically just proton) Number of each type of proton Clues about their environment Coupling/Splitting (typically just proton) Signal shape Number of protons on adjacent carbons

Chemical Shift TMS SiMe4 CHCl3 H2O

Integration Area underneath the peaks proportional to quantity of protons

TMS:water 2:1 TMS:water 6:1 TMS:water 1:1 TMS:water 1:6 TMS:water 1:2 The signal for TMS (SiMe4) and the signal for H2O both have the same integration (0.12). What is the ratio of TMS to water in this sample? TMS:water 2:1 TMS:water 6:1 TMS:water 1:1 TMS:water 1:6 TMS:water 1:2

TMS:water 2:1 TMS:water 6:1 TMS:water 1:1 TMS:water 1:6 TMS:water 1:2 The signal for TMS (SiMe4) and the signal for H2O both have the same integration (0.12). What is the ratio of TMS to water in this sample? TMS:water 2:1 TMS:water 6:1 TMS:water 1:1 TMS:water 1:6 TMS:water 1:2

Proton Relationship: Substitution Test Enantiomers S R Constitutional Isomers Same Substitution Results Relationship NMR Effect Same Compound Homotopic Same Chemical Shift Enantiomer Enantiotopic Same Chemical Shift Diastereomers Diastereotopic Diff. Chemical Shifts Constitutional Isomers Heterotopic Diff. Chemical Shifts

2 4 6 8 42 How many types of protons does 2-pentanol have? (How many signals do you expect?) 2 4 6 8 42

Proton Relationship: Substitution Test Same S R Diastereomers When there is a chiral center present, CH2’s are diastereotopic Substitution Results Relationship NMR Effect Same Compound Homotopic Same Chemical Shift Enantiomer Enantiotopic Same Chemical Shift Diastereomers Diastereotopic Diff. Chemical Shifts Constitutional Isomers Heterotopic Diff. Chemical Shifts

b a 1,4-dimethoxybenzene Ha Hb CHCl3 SiMe4 Downfield Deshielded Mention CHCl3 in CDCl3 Xylene Shifts 2.3 and 7.0 Upfield Shielded CHCl3 SiMe4

Upfield Shielded Downfield Deshielded Just a reminder about CHCl3

Aromatic Region Just a reminder about CHCl3

Benzene is 7.34. (CHCl3 appears at 7.2 ppm). Aromatic Region: 6.5-8.0 ppm Benzene is 7.34. (CHCl3 appears at 7.2 ppm). Strongly deshielded due to induced ring current and the right hand rule. External Magnetic Field Induced Magnetic Field That shields the interior of the ring, but deshields the exterior of the ring. Induced Ring Current Just a reminder about CHCl3

18 Annulene