CH 221 1st Edition Lecture 32 Outline of Last Lecture I. Radicals and FragmentsOutline of Current Lecture II. Mass SpectrumIII. Electromagnetic SpectrumIV. Stretching and Bending VibrationV. Hooke’s LawCurrent LectureII. Tallest peak in a mass spectrum is called the base peak- Base peak intensity is defined as 100%, all other peak intensities are measured relative to base peak- The way a molecule fragments in a mass spectrometer depends upon the bond strengths, stability of fragments, energy of electron beam hitting molecules, and structure of the molecule - To find m/z values, add mass of all atoms in the compoundIII. Electromagnetic spectrum- High frequency means short wavelength(λ) and high energy- Low frequency means long wavelength and low energy - E=hv=hc/λ- Wavenumber is measured in cm−1- Stretching vibration occurs along the line of a bondIV. Stretching can be symmetric or asymmetric- Bending can be symmetric in-plane (scissor), asymmetric in-plane (rock), symmetric out-of-plane (twist), or asymmetric out-of-plane (wag)- Stretching and bending vibration occurs at characteristic wavelengths- C=O approx. 1700cm−1- O-H approx. 3400cm−1- Functional group region (4000-1400cm−1)- Fingerprint region (1400-600cm−1)These 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.- The more polar the bond, the more intense the absorption will be- Most polar and intense O-H > N-H > C-H least polar and intenseV. Hooke’s law states that the lighter atoms show absorption bands at larger wavenumbers- C-H approx. 3000cm−1 C-D approx. 2200cm−1 C-O approx. 1100 cm−1 C-Cl approx. 700cm−1- Greater bond order, larger wavenumber- Electron delocalization (resonance) affects frequency of absorption - More double bond character means greater
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