Singlet

Opacity broadening Electromagnetic radiation emitted at a particular point in space can be reabsorbed as it travels through space. This absorption depends on wavelength. The line is broadened because the photons at the line center have a greater reabsorption probability than the photons at the line wings. What causes line broadening? In atomic physics, Doppler […]

Broad peaks can represent inhomogeneities in the magnetic field which may have been caused by poor shimming, paramagnetic materials in the sample or particulate matter. Alternatively, peaks can broaden due to exchange processes on the NMR time scale. What causes a broad singlet in NMR? Table NMR 1 summarizes coupling patterns that arise when protons […]

In addition, there are three common causes of line broadening: natural, Doppler, and pressure broadening. Natural broadening and the Uncertainty Effect: Natural broadening of pure spectral lines occurs due to the finite amount of time an atom spends in its excited electronic state. What factors contribute to the broadening of a spectral emission or absorption […]

A basic NMR line broadening experiment is to determine the rotational energy barrier of a certain chemical bond. If the bond rotates slowly enough compared to the NMR time scale (e.g., amide bond), two different species can be detected by the NMR spectrometer. What causes line broadening in NMR? Broad peaks can represent inhomogeneities in […]

For polymers however, resonance signals from repeating units often coalesce as broad peaks, even with high-field NMR spectrometers. This is largely due to poor molecular rotation and repeating units being situated in marginally different chemical environments. What causes a broad singlet in NMR? Table NMR 1 summarizes coupling patterns that arise when protons have different […]

Molecular oxygen is known to be an efficient quencher of the fluorescence of aromatic hydrocarbons (Berlman, 1965; Ware, 1962). The studies so far published show quenching by oxygen to be a diffusion-controlled process in which virtually every collision with the excited fluorophore is effective in quenching. What does quenching mean in chemistry? Chemical quenching means […]

The researchers used data on 13,800 twin births between 1967 and 1978 to show that females exposed in utero to a male twin are less likely to graduate from high school (-15.2 percent), to complete college (-3.9 percent) or to get married (-11.7 percent). What are the disadvantages of being twins? With twins, you’re at […]

We also found larger differences in IQ among the sons of mothers born before 1940. Conclusions: Twins and triplets fall slightly behind singletons in cognitive and physical development, even in early adulthood, but twins and triplets show no major differences. Do twins have lower IQ? On average, twins have lower IQ scores at 7 and […]

Children born as twins have a greater likelihood of poor neurodevelopmental outcomes compared to singletons when birth weight and gestational age are not controlled for (Lorenz, 2012). What are the disadvantages of being twins? With twins, you’re at greater risk for: Premature birth. Twins are born prematurely more than half the time. Low birth weight […]

For IQ scores, twins scored 0.09 points lower than non-twins at age 8 and 0.83 points lower at 10. However, twins scored higher at age 12 by 0.14 points. The only significant difference found was at age 10. Do twins have a lower IQ? On average, twins have lower IQ scores at 7 and 9 […]

While twins have been subjects in countless studies that try to separate the effects of nature from nurture, a recent study in PLOS ONE is the first to actually look at what being a twin means for life expectancy. Analysis shows that twins have lower mortality rates for both sexes throughout their lifetimes. What is […]

It revealed twins have twice the rate of late language emergence than singleton children; 38 per cent for twins compared to 19 per cent for singletons. In this study, 71 per cent of two-year-old twins were not combining words, compared to only 17 per cent of single-born children. Do twins have more developmental delays? Conclusions: […]

Description: A doublet of triplets (dt) is a pattern of two triplets, in a 1:1 ratio of relative intensities, that results from coupling to one proton (or other spin 1/2 nuclei) with a larger J value and two protons with a smaller J value. What causes a doublet of doublets in NMR? Explanation: A doublet […]

Broad peaks can represent inhomogeneities in the magnetic field which may have been caused by poor shimming, paramagnetic materials in the sample or particulate matter. Alternatively, peaks can broaden due to exchange processes on the NMR time scale. Why are alcohol NMR peaks broad? Because protons are shared to varying extent with neighboring oxygens, the […]

Conclusion: Twin fetus experience slowing of growth beginning at ∼26 weeks of gestation and a greater degree of asymmetric growth pattern compared with singletons. These findings suggest that the slower growth of twins may reflect a state of “relative growth restriction” compared with singleton gestations. Do twins grow as fast as singletons? Research has shown […]

If there is one hydrogen on the adjacent atoms, the resonance will be split into two peaks of equal size, a doublet. Two hydrogens on the adjacent atoms will split the resonance into three peaks with an area in the ratio of 1:2:1, a triplet. What does a triplet mean in NMR? Triplet: In NMR […]

The hydrogen atoms (protons) of ethanol occupy 3 different chemical environments so that the H-1 proton low resolution NMR spectra should show 3 peaks (diagram above). Note the ratio of the 3 colours for the 3 proton chemical environments in ethanol. Where does ethanol show up on NMR? Ethanol 1 H NMR spectrum (high res.) […]

Nuclei that possess an even number of both neutrons and protons have no spin (spin quantum number = 0) and are not NMR-active, for example 2He, 12C, 16O, 32S. Why is c12 Not NMR active? C NMR spectroscopy is much less sensitive to carbon than 1H NMR is to hydrogen since the major isotope of […]

All nuclei with an odd number of protons (1H, 2H, 14N, 19F, 31P) or nuclei with an odd number of neutrons (i.e. 13C) show the magnetic properties required for NMR. Only nuclei with even number of both protons and neutrons (12C and 16O) do not have the required magnetic properties. Which nuclei will show NMR […]

Selection Rules of electronic transitions transitions. Thus, S→S, T→T are allowed, but S→T, T→S are forbidden transitions. within a given set of p- or d-orbitals (i.e. those which only involve a redistribution of electrons within a given subshell) are forbidden. What are allowed and forbidden transitions in spectroscopy? specification of selection rule Selection rules, accordingly, […]