An enhanced Rotor Assisted Population Transfer (RAPT) experiment is presented and used as a simple and fast technique to measure the magnitude of the nuclear quadrupolar coupling constant of half-integer quadrupolar nuclei. The enhanced RAPT sequence consists of a train of Gaussian pulses with alternating off-resonant frequencies of +/-nuoff. Simulated and experimental results demonstrating the method are given in the case of 87Rb (spin 3/2) and 27Al (spin 5/2) nuclei. The RAPT sequence is also used to selectively suppress resonances based on their quadrupolar coupling constant.

The two-dimensional 17 O dynamic-angle spinning solid-state nuclear magnetic resonance spectrum of silica glass produced from the melt was measured. From this spectrum a three-dimensional histogram correlating 17 O chemical shift, quadrupolar coupling constant, and quadrupolar coupling asymmetry parameter for the bridging oxygen was obtained. Using existing correlations between NMR parameters and local structure, the distribution in quadrupolar coupling parameters was mapped into two-dimensional histograms correlating the Si-O-Si angle with Si-O distance, the Si-O-Si angle with Si-Si distance, and the Si-O distance with Si-Si distance. While the peak values for the Si-O-Si angle, the Si-O distance, and Si-Si distance distributions, at 147°, 1.59 Å, and 3.05 Å, respectively, are consistent within the precision of the NMR measurement with previous diffraction studies, the distribution widths are narrower than previous diffraction studies. The two-dimensional histogram reveals an unexpected strong positive correlation between the Si-O-Si angle and Si-O distance in the glass, running opposite to the trend generally found in crystalline silica polymorphs.

General chemistry courses predominantly use expository experiments that shape student expectations of what a laboratory activity entails. Shifting within a semester to course-based undergraduate research activities that include greater decision-making, collaborative work, and “messy” real-world data necessitates a change in student expectations and epistemology. Design considerations for laboratories that transition students and teaching assistants from one format to another are described here along with experiences when implemented in the second semester of a large-enrollment general chemistry course.

Pressure induced correlated evolution of the distributions of the Si–O distance and Si–O–Si inter-tetrahedral bond angle in vitreous silica quenched from pressures of up to ∼14 GPa at ambient temperature is measured in unprecedented detail using two-dimensional dynamic-angle-spinning 17O nuclear magnetic resonance spectroscopy. The results demonstrate that, in contrast to the conventional wisdom, vitreous silica undergoes irreversible structural changes even at pressures as low as ∼8 GPa. These structural changes at the short range involve a progressive reduction in the mean Si–O–Si angle and a broadening of the corresponding distribution, with increasing pressure. This bond angle reduction is accompanied by a concomitant monotonic increase in the mean Si–O distance. The mean values of the Si–O–Si angle and Si–O distance at various pressures closely follow the minimum in the corresponding potential energy surface calculated for the H6Si2O7 dimer molecule.

The swift conversion of chemistry courses to various online formats has presented challenges for students and instructors alike, with one of the most significant challenges being the logistics concerning online testing. At our institution, instructors of general, organic, and physical chemistry courses sought to balance issues of exam access, exam security, and continuity with a traditional test format when switching to unproctored online exams. Different approaches were utilized for exam delivery with varying success. Common challenges arose in several courses, such as the need to train students to use new technology, and the threat of online information for compromising exam security. The most successful attempts to meet these challenges, such as use of a test-bank, are consistent with reported best practices and suggest a way to maximize access, security, and continuity, while working to diminish technological and ethical pitfalls that accompany unproctored online exams.