IR/MS Analysis of the Hydroxybromination of Indene (1) Look at the mass spectrum

Question

IR/MS Analysis of the Hydroxybromination of Indene

(1) Look at the mass spectrum of the product. Identify the M+ peak, and describe two pieces of information that the mass spectrum provides that confirm the identity of the product.

(2) Describe the difference between the IR spectrum of your product, and that of the indene starting material. How can these spectra help you determine whether the reaction worked?

(3) Can the IR spectra help with determining the regioselectivity of the reaction (i.e. which isomer is formed)? Why/why not?

NMR Analysis

Here, you will identify which product isomer you formed by analyzing the 1H NMR spectrum in stages.

(4) There is a cluster of peaks in the 1H NMR spectrum between ? 7-8 ppm. Which hydrogen atoms in your product do those peaks correspond to, and why?

(5) Read p43 of this handout, and identify the peak in the 1H NMR spectrum corresponding to the OH hydrogen in the product.

(6) You have now assigned five of the protons in the molecule. Now, consider the peaks from ? 3-5.5 ppm labeled 1 - 4 in the 1H NMR spectrum. How many chemically inequivalent hydrogen atoms are left in this molecule? Explain how you determined your answer.

(7) a) Describe the coupling pattern (i.e. doublet, triplet, doublet of doublets etc) for the peak at ? 5.31, and calculate the coupling constant (J) value(s) (see p29, 31). Note - the 1H NMR spectrum was obtained on a 300 MHz spectrometer.

b) Describe the coupling pattern (i.e. doublet, triplet, doublet of doublets etc) for the peak at ? 4.29, and calculate the coupling constant (J) value(s).

c) Describe the coupling pattern (i.e. doublet, triplet, doublet of doublets etc) for the peak at ? 3.60, and calculate the coupling constant (J) value(s).

d) Describe the coupling pattern (i.e. doublet, triplet, doublet of doublets etc) for the peak at ? 3.25, and calculate the coupling constant (J) value(s).

(8) Using the coupling constants you calculated in Q7, identify which protons 1 - 4 couple to each other (i.e. does 1 couple with 2, etc). (9) I have labeled the 4 protons in the product Ha - Hd below. Ignoring the identity of X and Y (we'll get to that later) assign the 1H NMR spectrum (i.e. which of the numbered peaks 1-4 correspond to protons HA- D?). Use your answer to Q8 to help.

(9) I have labeled the 4 protons in the product Ha - Hd below. Ignoring the identity of X and Y (we'll get to that later) assign the 1H NMR spectrum (i.e. which of the numbered peaks 1-4 correspond to protons HA- D?). Use your answer to Q8 to help.

(10) An O atom is more electronegative than a Br atom. Look at the relative chemical shift of peaks 1-4 and identify the nature of X and Y in your product (i.e. is X OH or Br), and thus which isomer of bromoindanol you formed.

(11) Another (less effective) way to perform this reaction is to use hypobromous acid (Br-OH) as reagent. While the experimental procedure is more tedious than the method you used, the mechanism is easier to write. Write an arrow pushing mechanism for the reaction below, and explain why a single product is formed, and why that product is the one you characterized.

(12) We have been focused on regiochemistry so far. Based on the mechanism you drew in Q11 (and having read Klein p438), draw the actual product obtained, with the correct relative stereochemistry assigned. Explain why you chose that stereochemical outcome of the reaction.

Explanation / Answer

1) Look at the mass spectrum of the product. Identify the M+ peak, and describe two pieces of information that the mass spectrum provides that confirm the identity of the product.

Ans: There will be two peak of intensity 1:1 ratio , at M+ and M+2 (This is due to presence of bromine in the product)

The peaks will be at 212 and 214

(2) Describe the difference between the IR spectrum of your product, and that of the indene starting material. How can these spectra help you determine whether the reaction worked?

Answer: The IR spectrum of product will have a broad peak near 3400 cm^-1 due to -OH stretching which will be absent in the reactans (indane)

(3) Can the IR spectra help with determining the regioselectivity of the reaction (i.e. which isomer is formed)? Why/why not?

Ans: No it just gives idea about the functional groups as it is based on vibration of bonds. The vibrations will be independant of the opitcal properties.

NMR Analysis

Here, you will identify which product isomer you formed by analyzing the 1H NMR spectrum in stages.

(4) There is a cluster of peaks in the 1H NMR spectrum between 7-8 ppm. Which hydrogen atoms in your product do those peaks correspond to, and why?

Ans: The peaks near 7-8 ppm are due to aromatic hydrogen of benzene ring

(5) Read p43 of this handout, and identify the peak in the 1H NMR spectrum corresponding to the OH hydrogen in the product.

Ans : the peak should be near 3-4

(6) You have now assigned five of the protons in the molecule. Now, consider the peaks from 3-5.5 ppm labeled 1 - 4 in the 1H NMR spectrum. How many chemically inequivalent hydrogen atoms are left in this molecule? Explain how you determined your answer.

Answer: the given product consist of total protons = 9 protons

five are already assigned (aromatic (4) and -OH (1) )

Out of other four : two will be chemicall equivalent and two will be of other type (so there are three chemically equivalent protons)

(7) a) Describe the coupling pattern (i.e. doublet, triplet, doublet of doublets etc) for the peak at 5.31, and calculate the coupling constant (J) value(s) (see p29, 31). Note - the 1H NMR spectrum was obtained on a 300 MHz spectrometer.

Answer: Pages are not given

b) Describe the coupling pattern (i.e. doublet, triplet, doublet of doublets etc) for the peak at 4.29, and calculate the coupling constant (J) value(s).

c) Describe the coupling pattern (i.e. doublet, triplet, doublet of doublets etc) for the peak at 3.60, and calculate the coupling constant (J) value(s).

Answer: The peak at 3.6 will be doublet

d) Describe the coupling pattern (i.e. doublet, triplet, doublet of doublets etc) for the peak at 3.25, and calculate the coupling constant (J) value(s).

Answer : Doublet

(8) Using the coupling constants you calculated in Q7, identify which protons 1 - 4 couple to each other (i.e. does 1 couple with 2, etc). (9) I have labeled the 4 protons in the product Ha - Hd below. Ignoring the identity of X and Y (we'll get to that later) assign the 1H NMR spectrum (i.e. which of the numbered peaks 1-4 correspond to protons HA- D?). Use your answer to Q8 to help.

(9) I have labeled the 4 protons in the product Ha - Hd below. Ignoring the identity of X and Y (we'll get to that later) assign the 1H NMR spectrum (i.e. which of the numbered peaks 1-4 correspond to protons HA- D?). Use your answer to Q8 to help.

For question 8 and 9 we need data

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