CH 221 Edition 7 Lecture 34 Outline of Last Lecture I. UV/Vis spectrumOutline of Current LectureII. NMR Spectroscopy III. Diamagnetic ShieldingIV. Proton NMR SpectrumCurrent LectureII. NMR Spectroscopy - Ketone 1713 cm−1- Alcohol 3340 cm−1- NMR= Nuclear Magnetic Resonance- Identifies the carbon-hydrogen framework of a compound - NMR enables us to connect neighboring carbons- 1H was the first to be studied 1H NMR is proton magnetic resonance- Spin state of a nucleus is affected by an applied magnetic field- As a result of its charge, a nucleus with a spin has a magnetic moment and generates a magnetic field- If no applied magnetic field; magnetic moment of nuclei are randomly oriented- If applied magnetic field; magnetic moments will align either with or against applied field- Beta spin state high energy- Alpha spin state low energy - The difference in energy between two spin states depends on the strength of the appliedmagnetic field- All the hydrogen in a compound will not experience the same magnetic fieldeffective=¿ Bapplied+ BlocalB¿- Shielding varies around different hydrogens- Electrons surrounding the nucleus decrease the effective magnetic fieldThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.III. Diamagnetic Shielding- Chemically equivalent protons are protons in the same environment- An NMR spectrum exhibits a signal for each proton belonging to a different environment- Protons in electron rich environments are more shielded and appear at lower frequencies (right side of spectrum)- Protons in electron poor environments are less shielded and appear at higher frequencies (left side of spectrum) - Each set of chemically equivalent protons give a signal in the 1H NMR spectrum- Reference compound is a small amount of a compound added to a sample tube containing compound whose NMR spectrum is to be taken- Reference compound is tetramethylsilane aka TSM and has 0 ppmIV. 1H NMR Spectrum- Position at which a signal occurs in an NMR spectrum is called the chemical shift- Greater chemical shift = higher the frequency - Relative positions of signals - Electron withdrawal causes NMR signals to appear at higher
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