CHM1022 Lecture Notes - Lecture 11: Wavenumber, Mass Spectrum, Nuclear Magnetic Resonance

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azureraccoon117

26 Aug 2018

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Can you calculate molecular formula from it"s microanalysis result and determine number of dbe from molecular formula. Can you use ir spectroscopy to identify functional groups. Can you apply basic principles of 1 h and 13 c nmr spectroscopy to analyse nmr spectra. Index of hydrogen deficiency (aka double bond equivalents dbe) Indicates the amount of presence or unsaturation (double/triple bonds) If it equals 0, then there is no double/triple bonds, or ring. If it equals 1, it can indicate a ring or a double bond. Dbe formula x - (1/2)y - (1/2)z + 1 = no. of double/triple bonds and if a ring is present. Used to determine molecular weight of a compound. Process: a sample are passed through an electron beam. The molecules are: ionised (electrons are removed, so it becomes positive, broken into fragments. 2. the now charged molecules are separated before reaching the detector.

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Question 1: Watch the series of videos found here and hand in your responses to the red parts below:

https://www.youtube.com/watch?v=QSztChmDY44&list=PLaySzQJTCO1kxtP1zdoysPWoFmDHl2dLb

a. Spectroscopy (NMR, IR, Mass spec) Introduction (just watch the first 4 minutes, 45secs, the rest is an advertisement)

b. Proton NMR - How to Analyze the Peaks of H-NMR Spectroscopy (list the four factors covered in the video--i.e. the characteristics used to match the peaks to the regions of the molecule; watch the first 10 minutes, 32 seconds and move on to the next video)

c. Proton NMR Spectroscopy Analysis Using C3H7Cl (draw the H NMR spectrum and label it (hint: it corresponds to 1-chloropropane or 2-chloropropane); explain to me how symmetry, the number of types of hydrogens (peaks) and splitting patterns helped you to match the spectrum to the molecule you chose; watch the first 6 minutes, 10 seconds)

d. *H-NMR Example Matching The Molecule To The Graph (draw the H NMR spectrum, labeling the ordered peaks with integrals/heights, shifts (i.e. ppm), splitting (i.e. is it a singlet, doublet, etc. peak) and use arrows or labels to match the peaks with the corresponding H's on molecule A

e. *H-NMR Example (cont) Matching The Molecule To The Spectroscopy Graph (draw the correct H NMR spectrum, labeling the ordered peaks with integrals/heights, shifts (an estimate or range is ok), splitting (i.e. is it a singlet, doublet, etc. peak) use arrows or labels to match the peaks with the corresponding H's on molecules B, C, D, and E -

f. Degree of Unsaturation aka Index of Hydrogen Deficiency (tell me how you can determine whether there are pi bonds/rings, how do you know how many pi bonds; also how do Oxygen, Nitrogen and Halogens change the hydrogen count; what formula can you use to account for all these effects ; watch the first 15 minutes, 15 seconds) This is going to help you draw the molecule based on the molecular formula and spectroscopy

1.Structural isomer refers to organic compound that have the same molecular formula but different structure (bonding pattern is different). This problem is designed to guide you to explore structure isomer.

(a)Go ahead and write Lewis structure for butane (C₄H₁₀). You may draw four C atoms connect straight as like in train.

(b)In the above structure, four C atoms are connected straight in a line. If you move one C atom to the side (like 3 C atoms in a line, one connected to the middle C atom), after you supply all the H atoms to make all the C atoms saturated with 4-bonds each. Will the molecular formula for your structure drawn be different from butane?

( c) Structures you obtained in (a) and (b) are an example of structural isomers. What kind of name we can give to structure in (b) so we can differentiate it from structure in (a)?

2.Alkane is the basic building block of organic compound. We often write alkane chain as a group R. On this basic chain, we can add different functional group, like âOH for alcohol, -COOH for carboxylic acid.

(a)Methanol refers to CH₃OH. Ethanol refers to CH₃CH₂OH. Draw the Lewis structure for these two compounds.

(b) If you have a straight alkane chain, where does âOH group can be attached? How do you name it so you can know where âOH group is attached?

3. Give the Lewis structure for CH₃COOH. Give its systematic name and common name.

4. Ester refers to two alkane chains connected through a single O atom. Write the Lewis structure for this simplest kind of ester: CH₃OCH₃. Find its name and some common use.

5. Benzene molecular formula is C₆H₆. The six carbon atoms are connected to form a ring (hexagon). Draw the Lewis structure for C₆H₆. Do you think the six bond lengths between C-C atoms should be same or not according to your drawn Lewis structure?

CHM1022 Lecture Notes - Lecture 11: Wavenumber, Mass Spectrum, Nuclear Magnetic Resonance

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