Carbon ground state

We would normally write the electronic ground state electron configuration of a carbon atom as ls-2s 2p-. Despite the intellectual activity that has gone into defining mythical valence states for carbon atoms in different bonding situations, no one would include a d-orbital in the description of ground state carbon. 

Gomberg reaction, 333 Grignard reagents addition to 0=C—C=0, 201 addition to C=N, 244 addition to 0=0, 221,235, 238 structure, 221 Ground state carbon, 3 dienes, 13... 

Predict the products formed by reaction of ground-state carbon atoms with rw-2-butene and with trans-2-butene. 

FIGURE 11.11 Products formed in the reactions of ground state carbon atoms with unsaturated hydrocarbon molecules under single collision conditions via hydrogen atom elimination. Note that for the reaction of carbon atoms with acetylene, the tricarbon plus molecular hydrogen elimination channel was observed, too. 

The geometric deformation of molecules can also induce orbital distortions. Seebach and coworkers [IS] have shown that dioxanones 1 are distorted. In the ground state, carbon-4 is pyramidalized through the mean plane of the ring toward carbon-2. This distortion is enhanced in the transition state for a nucleophilic attack, so such reactions are stereoselective because of better overlap control (Figure L7). 

Orbital diagrams As mentioned earlier, electrons in orbitals can be represented by arrows in boxes. Each box is labeled with the principal quantum number and sublevel associated with the orbital. For example, the orbital diagram for a ground-state carbon atom, which contains two electrons in the Is orbital, two electrons in the 2s orbital, and one electron in two of three separate 2p orbitals, is shown below. 

Table n. OMuparison of Second-Order Rate Constants for tbe CoUisional Removal of Ground State Carbon, Silicon, and Germanium Atoms by Various Gases (S6) ... 

Ans. The atomic orbitals in the valence shell of an isolated ground-state carbon atom contains two paired electrons in the 2 s orbital and two unpaired electrons in each of two 2p orbitals. The 2s orbital is filled and there are two half-filled 2p orbitals together with an empty 2p orbital. This predicts incorrectly that the valence of carbon is 2. Carbon is tetravalent and, furthermore, the four bonds of carbon are equivalent. This is the situation for carbon atoms in alkanes (and also in diamond). The reality of carbon s four bonds requires that we postulate excitation of carbon to a different electronic structure prior to bond formation. The excitation involves two processes— promotion and hybridization (Fig. 11-2). Promotion is the unpairing of the two electrons in the 2s orbital by promotion of one of the electrons to a higher energy 2p orbital. The resulting electronic... 

Wave functions for the 2s, 2p,, 2py, and 2p orbitals of ground state carbon are mixed to form four new and equivalent 2s hybrid orbitals. 

The reaction of benzene with a ground state carbon atom,... 

Ground-State Carbon Orbitals. The carbon-atom orbiteils in the ground state can be visualized as shown graphically Fig. 2.6. The wave-function calculations represent the s orbital as a sphere with a blurred or fuzzy edge that is characteristic of all orbital representation. As a sphere, the s orbital is non-directional. The 2p orbital can be represented as an elongated barbell which is symmetrical about its axis and directional. 

Let us now expand the ground-state carbon orbitals in a minimal basis of GTOs with exponents chosen so as to match the expectation values of r given in Section 6.5.7. This prescription gives us the following basis functions... 

Table 8.2 The Gaussian (9s5p) exponents and expansion coefficients for the ground-state carbon otbitals...

Fig. 8.11. The radial distribution functions of the ANOs for the ground-state carbon atom. The Is, 2s and...

Table 8.10 The total energy of the ground-state carbon atom obtained in valence CISD calculations using natural orbitals Ec sd, using correlating orbitals optimized in a primitive GTO basis osd using numerical correlating orbitals Tbe eneigies are given in mEh...

In Table 8.14, we have listed the core-core, core-valence and valence-valence correlation energies of the ground-state carbon atom calculated using the basis sets cc-pVXZ and cc-pCVXZ. There are only small differences in the valence-valence correlation energies for the two basis sets - as we would expect since the cc-pVXZ sets have been designed specifically with the... 

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