The structure for the compound having molecular formula C 8 H 10 O is to be proposed based on the distinct signals in its 1 H NMR spectrum. Concept introduction: In 1 H NMR spectroscopy, protons in different environments within a molecule have different chemical shifts, that is, they experience different degrees of shielding. In addition to chemical shift, a 1 H NMR spectrum provides structural information based on the number of signals, which tells how many different kinds of protons are there; integrated areas, which tells the ratios of the various kinds of protons; and splitting pattern, which gives information about the number of protons that are within two or three bonds of the one giving the signal. Spin-spin splitting of NMR signals results from the coupling of the nuclear spins that are separated by two bonds (geminal coupling) or three bonds (vicinal coupling). In these cases, the number of peaks into which a signal is split is equal to (n+1) , where n is the number of protons to which the proton in question is coupled. Protons that have the same chemical shift do not split each other’s signals. Complicated splitting patterns can result when a proton is unequally coupled to two or more protons that are different from one another. The ideal range for alkane protons is δ 0.9 - δ 1.4 ; for alcohol, it is δ 2 - δ 5.0 , and for aromatic protons, it is δ 6.5 - δ 8.5 . The chemical shift of a signal prompts about the aromatic rings, double bonds, or nearby electronegative atoms. The integration of each signal suggests the number of protons responsible for that signal. The splitting pattern of a signal indicates the number of neighboring protons that are distinct from the protons responsible for that signal. To deduce the structure of an unknown compound, the first step is to find the index of hydrogen deficiency if the molecular formula is given. Based on the data given in the 1 H NMR, molecular fragments with multiple carbon atoms can be built.

Question

(a 4 shows scanning electron microscope (SEM) images of extruded actions of packing bed for two capillary columns of different diameters, al 750 (bottom image) and b) 30-μm-i.d. Both columns are packed with the same stationary phase, spherical particles with 1-um diameter. A) When the columns were prepared, the figure shows that the column with the larger diameter has more packing irregularities. Explain this observation. B) Predict what affect this should have on band broadening and discuss your prediction using the van Deemter terms. C) Does this figure support your explanations in application question 33? Explain why or why not and make any changes in your answers in light of this figure. Figure 4 SEM images of sections of packed columns for a) 750 and b) 30-um-i.d. capillary columns.³

Answer 1

Question

Chapter 16, Problem 16.32P

Interpretation Introduction

Interpretation:

The structure for the compound having molecular formula C8H10O is to be proposed based on the distinct signals in its 1H NMR spectrum.

Concept introduction:

In ^1HNMR spectroscopy, protons in different environments within a molecule have different chemical shifts, that is, they experience different degrees of shielding.

In addition to chemical shift, a 1H NMR spectrum provides structural information based on the number of signals, which tells how many different kinds of protons are there; integrated areas, which tells the ratios of the various kinds of protons; and splitting pattern, which gives information about the number of protons that are within two or three bonds of the one giving the signal. Spin-spin splitting of NMR signals results from the coupling of the nuclear spins that are separated by two bonds (geminal coupling) or three bonds (vicinal coupling). In these cases, the number of peaks into which a signal is split is equal to (n+1), where n is the number of protons to which the proton in question is coupled. Protons that have the same chemical shift do not split each other’s signals.

Complicated splitting patterns can result when a proton is unequally coupled to two or more protons that are different from one another.

The ideal range for alkane protons is δ 0.9- δ 1.4; for alcohol, it is δ 2- δ 5.0, and for aromatic protons, it is δ 6.5- δ 8.5.

The chemical shift of a signal prompts about the aromatic rings, double bonds, or nearby electronegative atoms. The integration of each signal suggests the number of protons responsible for that signal. The splitting pattern of a signal indicates the number of neighboring protons that are distinct from the protons responsible for that signal. To deduce the structure of an unknown compound, the first step is to find the index of hydrogen deficiency if the molecular formula is given. Based on the data given in the 1H NMR, molecular fragments with multiple carbon atoms can be built.

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