Molecule condensed structures

Since the six carbons shown above have 10 additional bonds, the variety of substituents they carry or the structures they can be a part of is quite varied, making the Diels-Alder reaction a powerful synthetic tool in organic chemistry. A moment s reflection will convince us that a molecule like structure [XVI] is monofunctional from the point of view of the Diels-Alder condensation. If the Diels-Alder reaction is to be used for the preparation of polymers, the reactants must be bis-dienes and bis-dienophiles. If the diene, the dienophile, or both are part of a ring system to begin with, a polycyclic product results. One of the first high molecular weight polymers prepared by this synthetic route was the product resulting from the reaction of 2-vinyl butadiene [XIX] and benzoquinone [XX] ... 

Organic molecules are usually drawn using either condensed structures or skeletal structures. In condensed structures, carbon-carbon and carbon-hydrogen bonds aren t shown. In skeletal structures, only the bonds and not the atoms are shown. A carbon atom is assumed to be at the ends and at the junctions of lines (bonds), and the correct number of hydrogens is menially supplied. 

Write the condensed structural formulas and molecular formulas for the following molecules. The reactive groups are shown in red. 

Hydrogen bonds can exist in many molecules other than HF, H20, and NH3. The basic requirement is simply that hydrogen be bonded to a fluorine, oxygen, or nitrogen atom with at least one unshared pair. Consider, for example, the two compounds whose condensed structural formulas are... 

Two-dimensional structural diagrams of organic compounds, such as condensed structural diagrams and line structural diagrams, work well for flat molecules. As shown in the table above, however, molecules containing single-bonded carbon atoms are not flat. 

Draw a condensed structural diagram for each molecule. 

The two molecules in Figure 6-4 are not different isomers they are both butane. Despite the crooked CCCC chain of the molecule on the right, it still has the same condensed structural formula, as shown in Figure 6-5. 

Due to Heisenberg s uncertainty and Pauli s exclusion principles, the properties of a multifermionic system correspond to fermions being grouped into shells and subshells. The shell structure of the one-particle energy spectrum generates so-called shell effects, at different hierarchical levels (nuclei, atoms, molecules, condensed matter) [1-3]. 

Throughout this chapter, both expanded and condensed structural formulas are used. Molecules may even be shown using both the condensed and expanded forms for different parts of the molecule. Rather than adhere to using one structural formula, our goal is to represent the basic structure of the molecule. 

You can refer to the same molecule in a number of different ways. For example, you can refer to pentane by its name (ahem. .. pentane)] by its molecular formula, CjHj2 or by the complete structure in Figure 6-2. Clearly, these names include different levels of structural detail. A condensed structural formula is another naming method, one that straddles the divide between a molecular formula and a complete structure. For pentane, the condensed structural formula is CH3CH2CH2CH2CH3. This kind of formula assumes that you understand how straight-chain alkanes are put together. Here s the lowdown ... 

Molecular formulas merely include the kinds of atoms and the number of each in a molecule (as C4H , for butane). Structural formulas show the arrangement of atoms in a molecule (see Fig. 1-1). When unshared electrons are included, the latter are called Lewis (electron-dot) structures [see Fig. 1-1(/)]. Covalences of the common elements—the numbers of covalent bonds they usually form—are given in Table 1-1 these help us to write Lewis structures. Multicovalent elements such as C, O. and N may have multiple bonds, as shown in Table 1-2. In condensed structural formulas all H s and branched groups are written immediately after the C atom to which they are attached. Thus the condensed formula for isobutane [Fig. l-l(f>)) is CH,CH(CH,)... 

In the condensed phase, due to interactions of molecules with neighbouring species, no single instrument, regardless of its resolution, can record a spectrum in which individual transitions are seen. In the best case for simple molecules, fine structure corresponding to envelopes of transitions can be observed (Fig. 11.1). 

The condensed structure of an organic molecule implies nothing about three-dimensional shape it only indicates the connections among atoms. Thus, a molecule can be arbitrarily drawn in many different ways. The branched-chain alkane called 2-methylbutane, for instance, might be represented by any of the following structures. All have four carbons connected in a row, with a -CH3 branch on the second carbon from the end. 

The following condensed structures have the same formula, C8H18. Which of them represent the same molecule ... 

Even condensed structures are awkward for cyclic molecules, and a streamlined way of drawing structures is often used in which cycloalkanes are represented by polygons. A triangle represents cyclopropane, a square represents cyclobutane, and so on. Carbon and hydrogen atoms aren t shown explicitly in these structures. A carbon atom is simply understood to be at every junction of lines, and the proper number of hydrogen atoms needed to give each carbon four bonds is supplied mentally. Methylcyclohexane, for instance, looks like this ... 

Nonbonded electrons are / v / usually not shown in condensed structures. Atoms in organic molecules (except hydrogen) generally obey the octet rule, so any atom with fewer than four bonds must have a number of non-bonded electron pairs equal to four minus the number of bonds. For example, the oxygen in an alcohol has 4 — 2 = 2 nonbonded electron pairs. 

From the 3D Models of n-pentane, isopentane, and neopentane (eChapter 23.4) draw expanded and condensed structures for each molecule. Name these molecules using proper IIUPAC nomenclature. 

Each of the three fractions contain a number of sequences that are sometimes called junk and can represent, for example, viruses that found their way into DNA in the past but were inactivated, leading to the fact that these sequences remain in the genome, but never express themselves. All of this DNA must be highly condensed. The DNA in each chromosome is a single molecule, on the order of several centimeters in length the total DNA in a eukaryotic cell is as much as three meters long. This DNA must be condensed so as to fit into a nucleus that is about 10 5 meters (lOvm) in diameter. The condensed structure of eukaryotic DNA is called chromatin. 

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