Structure, condensed line-bond

In Summary Determination of organic structures relies on the use of several experimental techniques, including elemental analysis and various forms of spectroscopy. Molecular models are useful aids for the visualization of the spatial arrangements of the atoms in structures. Condensed and bond-line notations are useful shorthand approaches to drawing two-dimensional representations of molecules, whereas hashed-wedged fine formulas provide a means of depicting the atoms and bonds in three dimensions. 

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. 

Straight-chain alkane, 80 Strecker synthesis, 972 Structure, condensed, 22 electron-dot, 9 Kekule, 9 Lewis, 9 line-bond, 9 skeletal, 23... 

You should be able to draw chemical formulas that show all of the valence electrons in a molecule (Lewis structures), using lines for bonds and dots to show unshared electrons. You should be proficient in representing structures as dash structural formulas, condensed structural formulas, and bond-line structural formulas. In particular, the more quickly you become skilled at using and interpreting bondline formulas, the faster you will be able to process structural information in organic chemistry. You have also learned about resonance structures, the use of which wiU help us in understanding a variety of concepts in later chapters. 

Write condensed and bond-line structural formulas for all of the constitutional isomers PRACTICE PROBLEM 4.1 with the molecular formula CyH-ie. (There are a total of nine constitutional isomers.)... 

Condensed and bond-line formulas are abbreviated representations of molecules. Hashed-wedged line drawings illustrate molecular structures in three dimensions. 

For each condensed formula, draw a line-bond structure of the anion, and next to it draw the +1 counterion as a separate ion. 

B) This condensed structural diagram shows only carbon-carhon bonds. (C) This line structural diagram uses lines to depict carbon-carbon bonds. 

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. 

The first of the abbreviated structural formulae has the formula condensed on to one line. These formulae can be difficult to write, particularly for branched molecules. As you can see, the second abbreviated structural formula shows all the carbon-to-carbon bonds and the branches can be clearly seen. If you are asked to draw an abbreviated structural formula, then it is advisable to use the second of these two types. 

When an ionic organic reaction (the kind catalyzed by most enzymes) occurs a nucleophilic center joins with an electrophilic center. We use arrows to show the movement of pairs of electrons. Tire movement is always away from the nucleophile which can be thought of as "attacking" an electrophilic center. Notice the first step in the second example at right. The unsaturated ketone is polarized initially. However, this is not shown as a separate step. Rather, the flow of electrons from the double bond, between the a- and (1-carbons into the electron-accepting C=0 groups, is coordinated with the attack by the nucleophile. Dotted lines are often used to indicate bonds that will be formed in a reaction step, e.g., in an aldol condensation (right). Dashed or dotted lines are often used to indicate partially formed and partially broken bonds in a transition state, e.g., for the aldol condensation (with prior protonation of the aldehyde). However, do not put arrows on transition state structures. 

Write an expanded structural formula with a line for each bond (like the formulas on p. 32) for each of the following substances which are represented by a condensed formula ... 

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 ... 

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