01252010 - CH 310N MWF 8:00 Lecture 3 M 1/25/2010 Reading...

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CH 310N – MWF 8:00 – Lecture 3 – M 1/25/2010 Graded Homework : HW#01 deadline = 4:00 p.m. on Th 1/28 HW#02 deadline = 2:00 p.m. on F 1/29 Reading Assignment : Sections 13.5, 13.6, 13.7 Textbook Problems : None today… Last Time : Introduction to spectroscopy Infrared spectroscopy (Chapter 12) Today : Suzette Ruedas sent out the e-mail with the link to the Health Professions Survey on Friday afternoon. Please complete this survey ASAP if you have not already done so. If you do not complete this survey, we will not be able to assign you a mentor for shadowing!!! If you have an excusable conflict for ANY of the three midterm exams, the deadline to sign up to take a conflict exam is 5:00 p.m. on Friday, February 5 . Infrared spectroscopy continued (end Chapter 12) Introduction to NMR spectroscopy (begin Chapter 13) TA office hours and discussion sessions begin this week. See the “I Need Help!!!” page on Blackboard for complete details…
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Mass effect? Consider two identical springs, one attached to a heavy weight, the other attached to a light weight. Which spring should vibrate faster? The one attached to the light weight Bond strengths (“spring tension”) typically do not change very much upon isotopic substitution. Typical C–H stretch Typical C–D stretch Which should have the higher vibrational frequency? (3000 cm –1 ) (2200 cm –1 ) When 2 atoms differ significantly in mass, the stretching frequency is controlled primarily by the lighter atom all hydrogen stretching absorptions appear in the same region of an IR spectrum Types of vibration? Stretching – occurs along the line of the chemical bond Bending – any vibration not along the line of a bond (for instance, like a pendulum swinging back and forth) In general, bending vibrations occur at lower frequencies than stretching vibrations
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Textbook Figure 12.3
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Allowed vibrations are termed normal vibrational modes . A diatomic molecule (like H–F) can only undergo stretching vibrations. Bending vibrations become possible in more complicated molecules Let’s consider the kinds of vibrations possible for a methylene (–CH 2 –) group. These are illustrative of the kinds of vibrations expected for other fragments in organic molecules. (See Figure 12.3 in the text) Symmetric stretch Asymmetric stretch Symmetric, in-plane bend (scissor) Asymmetric, in-plane bend (rock) Symmetric, out-of-plane bend (wag)
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01252010 - CH 310N MWF 8:00 Lecture 3 M 1/25/2010 Reading...

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