Quartets

Higgins J, Ernst W E, Caiiegari C, Reho J, Lehmann K K, Scoies G and Gutowski M 1996 Spin poiarized aikaii ciusters observation of quartet states of the sodium trimer Phys. Rev. Lett. 77 4532... 

As discussed in preceding sections, FI and have nuclear spin 5, which may have drastic consequences on the vibrational spectra of the corresponding trimeric species. In fact, the nuclear spin functions can only have A, (quartet state) and E (doublet) symmetries. Since the total wave function must be antisymmetric, Ai rovibronic states are therefore not allowed. Thus, for 7 = 0, only resonance states of A2 and E symmetries exist, with calculated states of Ai symmetry being purely mathematical states. Similarly, only -symmetric pseudobound states are allowed for 7 = 0. Indeed, even when vibronic coupling is taken into account, only A and E vibronic states have physical significance. Table XVII-XIX summarize the symmetry properties of the wave functions for H3 and its isotopomers. 

As with the other sem i-cm pineal methods. HyperGhem s im p le-meiitation of ZINDO/1 is restricted to spin multiplicities up to a quartet state. ZIXDO/1 lets you calculate the energy slates in molecules containing transition metals. 

Fig. 10.20 Schematic illustration of the creation of a multiple sequence alignment for five sequences A-E. In the fi step sequences C and E are aligned. In the second step sequences A and D are aligned. In the third step the pair Cl aligned with the pair AD. Finally, the quartet CEAD is aligned with B.

The above treatment of a three-eleetron ease shows how to generate quartet (spin states are named in terms of their spin degeneraeies 2S+1) and doublet states for a eonfiguration of the form... 

Is2s3s. Not all three-eleetron eonfigurations have both quartet and doublet states for example, the Is 2s eonfiguration only supports one doublet state. The methods used above to generate S = 3/2 and... 

One ean immediately identify the wavefunetions for two of the quartets (they are single entries) ... 

It only remains to eonstmet the doublet states whieh are orthogonal to these quartet states. Reeall that the orthogonal eombinations for systems having three equal eomponents (for... 

MHz H NMR spectrum of 1 1 dichloroethane (CI2CHCH3) showing the me thine proton as a quartet and the methyl protons as a doublet The peak multiplici ties are seen more clearly in the scale expanded insets... 

These three protons split the signal for the methme proton into a quartet... 

These eight combinations cause the signal of the CHCI2 proton to be split into a quartet m which the intensities of the peaks are m the ratio 13 3 1... 

FIGURE 13 15 The 200 MHz H NMR spectrum of ethyl bromide (BrCH2CH3) showing the char acteristic triplet-quartet pattern of an ethyl group The small peak at 8 1 6 is an impurity... 

Section 13 8 The methyl protons of an ethyl group appear as a triplet and the meth ylene protons as a quartet in compounds of the type CH3CH2X... 

H NMR spectrum of 2 butanone The triplet-quartet pattern of the ethyl group IS seen more clearly in the expanded scale insets... 

Compounds A and B are isomenc diketones of molecular formula CgHjQ02 The H NMR spectrum of compound A contains two signals both singlets at 8 2 2 (six protons) and 2 8 (four protons) The H NMR spectrum of compound B contains two signals one at 8 1 3 (triplet six protons) and the other at 8 2 8 (quartet four protons) What are the structures of compounds A and B" ... 

Treatment of 2 butanone (1 mole) with Br2 (2 moles) in aqueous HBr gave C4HgBr20 The H NMR spectrum of the product was charactenzed by signals at 8 1 9 (doublet three protons) 4 6 (singlet two protons) and 5 2 (quartet one proton) Identify this compound... 

NMR Chemical shift differences m their H NMR spectra aid the structure deter mmation of esters Consider the two isomeric esters ethyl acetate and methyl propanoate As Figure 20 9 shows the number of signals and their multiplicities are the same for both esters Both have a methyl singlet and a triplet-quartet pattern for their ethyl group... 

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