A comprehensive Raman spectroscopic/electronic structure study of hydrogen bonding by pyrimidine with eight different polar solvents is presented. Raman spectra of binary mixtures of pyrimidine with methanol and ethylene glycol are reported, and shifts in ν1, ν3, ν6a, ν6b, ν8a, ν8b, ν9a, ν15, ν16a, and ν16b are compared to earlier results obtained for water. Large shifts to higher vibrational energy, often referred to as blue shifts, are observed for ν1, ν6b, and ν8b (by as much as 14 cm(-1)). While gradual blue shifts with increasing hydrogen bond donor concentration are observed for ν6b and ν8b, ν1 exhibits three distinct spectral components whose relative intensities vary with concentration. The blue shift of ν1 is further examined in binary mixtures of pyrimidine with acetic acid, thioglycol, phenylmethanol, hexylamine, and acetonitrile. Electronic structure computations for more than 100 microsolvated structures reveal a significant dependence of the magnitude of the ν1 blue shift on the local microsolvation geometry. Results from natural bond orbital (NBO) calculations also reveal a strong correlation between charge transfer and blue shifting of pyrimidine's normal modes. Although charge transfer has previously been linked to blue shifting of the X-H stretching frequency in hydrogen bond donors, here, a similar trend in a hydrogen bond acceptor is demonstrated.

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b S Supporting Information T he physical chemistry laboratory course is an essential experience to the student wishing to pursue an advanced degree in chemistry or a career in a chemistry related field. A study in 2004 on physical chemistry curriculum points out that physical chemistry bridges physics, chemistry, and mathematics and develops complex critical-thinking skills required by scientists working on projects with interdisciplinary foci. 1 Physical chemistry now encompasses subareas too numerous to list and contributes to the study of almost all the other disciplines in chemistry. Today in a growing number of universities, however, the physical chemistry lab has been scaled back from the traditional two-semester period to just one semester. For example, in a recent informal survey of chemistry programs in the Southern Universities Group, approximately a quarter of the schools now only require one semester of physical chemistry lab to obtain a B.S. degree in chemistry. The loss of a whole semester has different roots, such as the desire to reduce the number of hours in a major or to make room for other new specialty courses such as environmental or forensic chemistry. The problem, therefore, arises in being able to provide students with enough lab experience to encompass the important areas of physical chemistry. Moore pointed out that it is extremely important to make sure the physical chemistry curriculum reflects what physical chemists really do. 2 With this in mind, in 1999, the University of Maryland integrated a program of physical and analytical techniques to investigate significantly more complex systems than those incorporated with one curriculum. 3 In 2004, Grand Valley State University sought to incorporate both computational and traditional physical chemistry laboratories in their curriculum, stating that the coupling of laboratories allows students to experience an experiment from a macroscopic, empirical point of view as well as an abstract, theoretical level that considers molecular-level events. 4 Combining multiple laboratory procedures into fewer multidimensional lab exercises allows students to be provided with opportunities encompassing multiple facets of physical chemistry in a constrained time frame. 5 Constructing a binary liquidÀvapor phase diagram is a classic physical chemistry experiment that is still taught in many chemistry departments and serves to illustrate an important physical concept. Here, we show that two other important concepts can be taught concurrently in this laboratory exercise, specifically molecular spectroscopy and quantum chemistry.The classic binary liquidÀvapor phase diagram experiment utilizes Raoult's law, which states that vapor pressure of an ideal solution is directly proportional to the mole fraction of each component. This law is a good approximation for a component only when its mole fraction is close to unity. Deviations, positive or negative, from Raoult's law give insight into the thermodynamic properties of the components involved. There have been...

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