Types of Carbon Atoms

In most paraffins there will be different numbers of hydrogens attached to the carbon atoms. There are four types of carbon atoms with names corresponding to the number of bonds made with other carbon atoms or functional groups. These names are primary, secondary, tertiary, and quaternary, as shown above. In a compound such as isopentane, there are three primary carbon atoms, one secondary, and one tertiary. 

Chlorine reacts with a hydrocarbon by substituting for one or more hydrogens. The easiest hydrogen to remove in this manner is from a tertiary carbon, next a secondary, and the least readily from a primary carbon. Where more than one type of carbon is present, as in isopentane, a mixture of compounds containing chlorine will be produced. 

Paraffins react with chlorine under the influence of light, heat, or catalysts to form chlorocarhons. The chlorocarhons are important in industry because of their own properties and because of their use as chemical intermediates in the synthesis of other compounds. Today, many of the chlorocarbons are regulated by federal and state agencies to limit their use because of detrimental effects on health and the environment. 

---

The changes of three types of carbon atoms can be monitored during processing with this method ... 

Just as chemical shifts in H NMR are measured relative to the protons of tetramethylsi lane chemical shifts m NMR are measured relative to the carbons of tetramethylsilane Table 13 3 lists typical chemical shift ranges for some representative types of carbon atoms In general the factors that most affect chemical shifts are... 

Quantum mechanical calculations generally have only one carbon atom type, compared with the many types of carbon atoms associated with a molecular mechanics force field like AMBER. Therefore, the number of quantum mechanics parameters needed for all possible molecules is much smaller. In principle, very accurate quantum mechanical calculations need no parameters at all, except fundamental constants such as the speed of light, etc. 

The above-mentioned alcohols are by far the most common. Butyl alcohol is not as commonly used as the first four in the series, but it is used. Secondary butyl alcohol and tertiary butyl alcohol, so named because of the type of carbon atom in the... 

The INEPT experiment can be modified to allow the antiphase magnetization to be precessed for a further time period so that it comes into phase before data acquisition. The pulse sequence for the refocused INEPT experiment (Pegg et al., 1981b) is shown in Fig. 2.13. Another delay, A. is introduced and 180° pulses applied at the center of this delay simultaneously to both the H and the C nuclei. Decoupling during data acquisition allows the carbons to be recorded as singlets. The value of Z), is adjusted to enable the desired type of carbon atoms to be recorded. Thus, with D, set at V4J, the CH carbons are recorded at VsJ, the CH2 carbons are recorded and at VeJ, all protonated carbons are recorded. With D3 at %J, the CH and CH ( carbons appear out of phase from the CH2 carbons. 

Carbon-13 nuclei, due to their low natural abundance, do not interact with each other in a molecule, though they are affected by adjacent protons. In practice, such couplings are removed by irradiation of the whole spectrum as it is recorded, in a technique known as proton noise decoupling. This means that practical NMR spectra exhibit one unsplit signal for each type of carbon atom present in the sample. 

Organic compounds contain four types of carbon atom methyl, methylene, methine and quaternary. And so if we simply record the spectrum as we would a proton spectrum, the result will be a series of quartets, triplets, doublets and singlets, each associated with a carbon-proton one-bond coupling constant of between 125 and 250 Hz. If we are dealing with a complex molecule, these multiplets will overlap and give us spectra which are almost impossible to analyse. In addition, coupling interactions over two or more bonds complicate the picture still further. 

This gives us the chemical shift information for each type of carbon atom in the molecule. We do not have any coupling information, however, but we shall see below how we can obtain the coupling information we need. 

Cyclodecane molecule is a typical representative of the medium ring. While in cyclohexane all carbon atoms are equivalent, in cyclodecane we have three types of carbon atoms and hydrogen atoms occupy six different positions unlike cyclohexane where we have only two positions, axial and equatorial. 

Fragments may be as fundamental as certain types of carbon atoms or hydrogen atoms, or may refer to multiple atom groupings such as -OH or -C-NH2... 

In the systems that I have examined, I can satisfy the dynamic requirements with a ten second pulse delay. The longest methyl T] may be 3 seconds. In general, the longer the side chain, the longer will be the methyl Tj. We will hear more about this subject later on. We need not be too concerned about NOE factors because they are usually full under the experimental conditions (T = 120-130°C) used for polymer quantitative measurements. The Tj problem can be handled, even under non-equilibrium conditions, by utilizing resonances from the same types of carbon atoms in a quantitative treatment. Such an approach can sometimes lead to more efficient quantitative NMR measurements. Adequate pulse spaclngs will have to be used whenever one wishes to utilize all of the observed resonances. Quantitative measurements in branched polyethylenes are very desirable because this is one of the best applications of analytical polymer C-13 NMR. 

But GO is also an archetype for more complex polyols. Catalytic hydrogenolysis of polyols leads to C-C and C-0 bond cleavage as well as activation via dehydrogenation of HCOH to C=0 sites (8, 9). With its three vicinal hydroxyl groups, and its two types of carbon atoms (all bearing hydroxyl functionalities) GO can serve as a simple model in which to study the competition between these processes. We aim to gain insight into the individual steps and apply that information to increase selectivity toward desired products. 

The H s attached to these types of carbon atoms are also called primary, secondary and tertiary (1 , 2 and 3°). respectively. A quaternary C is bonded to four other C s. 

A carbon atom is classified as primary (1°), secondary (2°), tertiary (3°) and quaternary (4°) depending on the number of carbon atoms bonded to it. A carbon atom bonded to only one carbon atom is known as 1° when bonded to two carbon atoms, it is 2° when bonded to three carbon atoms, it is 3°, and when bonded to four carbon atoms, it is known as 4°. Different types of carbon atom are shown in the following compound. 

The above-mentioned alcohols are by far the most common. Butyl alcohol is not as commonly used as die first four in die series, but it is used. Secondary butyl alcohol and tertiary butyl alcohol, so named because of the type of carbon atom in the molecule to which the hydroxyl radical is attached, must be mentioned because they are flammable liquids, while isobutyl alcohol has a flash point of 100°F. All of the alcohols of the first four carbon atoms in the alkanes, therefore, are extremely hazardous because of their combustion characteristics. 

DEPT uses a pulse sequence that includes a delay between the excitation pulse and the detection of the emission signal from the carbon atoms which is related to the C-H coupling constant, in order to distinguish between the different types of carbon atom (we do not need to understand how this is achieved). 

Hybridization. The simplest way to think about bonding in [1.1.1 Jpropellane is to characterize the state of hybridization at the two types of carbon atoms and then combine the hybrids pairwise into localized bond orbitals. In ordinary molecules, these have electron occupancy close to two, and the corresponding antibonds are nearly unoccupied. Bond delocalization can then be introduced by considering interactions of the occupied localized bond orbitals with the unoccupied localized antibond orbitals. 

Fig. 79. I3C NMR spectra showing that when 2-methylpropene (isobutene) is intercalated in a synthetic hectorite r-butanol is formed when the guest species reacts with the interlamellar water. The peaks labeled 1 and 2 refer to the two distinct types of carbon atom in r-butanol (453).

The interactions between the thiol alligator clips of methanethiol or benzenethiol and an Au nanoparticle containing 13 atoms, Aui3, was simulated using DFT.63 Calculations showed significant structural modifications occurred when the thiolate formed a bond to the Au cluster. Carrying out the calculations with the limited-size cluster allowed simplification of the problem. The type of carbon atom to which the S atom was bound did not make much difference in the bonding of the S atom to the Auu cluster. 

Amorphous carbon is a general term that covers non-crystalline forms of carbon such as coal, coke, charcoal, carbon black (soot), activated carbon, vitreous carbon, glassy carbon, carbon fiber, carbon nanotubes, and carbon onions, which are important materials and widely used in industry. The arrangements of the carbon atoms in amorphous carbon are different from those in diamond, graphite, and fullerenes, but the bond types of carbon atoms are the same as in these three crystalline allotropes. Most forms of amorphous carbon consist of graphite scraps in irregularly packing. 

The spin-lattice relaxation process, designated 7 (also termed longitudinal relaxation), varies widely for different types of carbon atoms. 

There are two types of carbon atom aromatic (Car) and aliphatic (Cai). Figure 1 shows that good correlation can be ob-... 

Classification of alcohols. Alcohols are classified according to the type of carbon atom (primary, secondary, or tertiary) bonded to the hydroxyl group. Phenols have a hydroxyl group bonded to a carbon atom in a benzene ring. 

Use the number of peaks and their chemical shifts in a 13C NMR spectrum to determine the number of types of carbon atoms in the compound and what functional groups they might represent. 

---