Answer to Question #286203 in Organic Chemistry for Gionny barscalli

Question

The measured integration trace gives the ratio 0.90 to 0.45 to 2.70 to 1.35 for the peak at &= 1.52 , 1.39 , 1.21 and 0.93 , respectively. Use the table below to answer the following questions.

• chemical shift (ppm) 0.5-5.0 and Description of H atom is ROH.
• chemical shift (ppm) 0.7-1.3 and description of H atom is RCH3.
• chemical shift (ppm)1.4-1.7 and description of H atom is R3CH.
• chemical shift (ppm) 1.2 -1.4 and description of H atom is R2CH2.
• chemical shift (ppm) is 2.1-2.6 and the description of H atom is RCH2CO.
• chemical shift (ppm) is 3.1-4.2 and description of H atom is RCH2Br or RCH2CI.
• chemical shift (ppm) is 9.0 -10.0 and the description of H atom is RCOH.
• chemical shift (ppm) is 10.0-12.0 and the description of H atom is RCOOH

question

a) what compound is responsible for the signal at & =0 (1 mark)

b) How many different types of proton are present in compound Z? (1 mark)

Answer 1

1a) C2H4O ( Acetaldehyde); In nuclear magnetic resonance (NMR) spectroscopy, the chemical shift is the resonant frequency of a nucleus relative to a standard in a magnetic field. Often the position and number of chemical shifts are diagnostic of the structure of a molecule.^[1][2][3] Chemical shifts are also used to describe signals in other forms of spectroscopy such as photoemission spectroscopy.

Some atomic nuclei possess a magnetic moment (nuclear spin), which gives rise to different energy levels and resonance frequencies in a magnetic field. The total magnetic field experienced by a nucleus includes local magnetic fields induced by currents of electrons in the molecular orbitals (note that electrons have a magnetic moment themselves). The electron distribution of the same type of nucleus (e.g. ¹H, ¹³C, ¹⁵N) usually varies according to the local geometry (binding partners, bond lengths, angles between bonds, and so on), and with it the local magnetic field at each nucleus. This is reflected in the spin energy levels (and resonance frequencies). The variations of nuclear magnetic resonance frequencies of the same kind of nucleus, due to variations in the electron distribution, is called the chemical shift. The size of the chemical shift is given with respect to a reference frequency or reference sample (see also chemical shift referencing), usually a molecule with a barely distorted electron distribution.

Acetaldehyde is a widespread, naturally occurring, colorless and flammable liquid with a suffocating smell. Acetaldehyde is found in various plants, ripe fruits, vegetables, cigarette smoke, gasoline and diesel exhaust. This substance is widely used in the manufacture of acetic acid, perfumes, dyes and drugs, as a flavoring agent and as an intermediate in the metabolism of alcohol. Acute exposure to its vapors results in irritation of the eyes, skin, and respiratory tract. Acetaldehyde is reasonably anticipated to be a human carcinogen. (NCI05)

1B) 3:1:3:3:4 are many different types of proton present in compound Z

ll protons in all organic molecules had the same resonance frequency in an external magnetic field of a given strength, the information in the previous paragraph would be interesting from a theoretical standpoint, but would not be terribly useful to organic chemists. Fortunately for us, however, resonance frequencies are not uniform for all protons in a molecule. In an external magnetic field of a given strength, protons in different locations in a molecule have different resonance frequencies, because they are in non-identical electronic environments. In methyl acetate, for example, there are two ‘sets’ of protons. The three protons labeled H_a have a different - and easily distinguishable – resonance frequency than the three H_b protons, because the two sets of protons are in non-identical environments: they are, in other words, chemically nonequivalent