Structural formulas, bond-line formula

The most common type of structural formula used by organic chemists, and the fastest to draw, is the bond-line formula. (Some chemists call these skeletal formulas.) The formula in Fig. 1.3 is a bond-line formula for propyl alcohol. The sooner you master the use of bond-line formulas, the more quickly you will be able to draw molecules when you take notes and work problems. And, lacking all of the symbols that are explicitly shown in dash and condensed structural formulas, bond-line formulas allow you to more quickly interpret molecular connectivity and compare one molecular formula with another. 

Molecular Formula Condensed Structural Formula Bond-Line Formula mp rc) bp rc) (1 atm) Density (g mL-1) Index of Refraction (no 20X)... 

Electron dot formulas are useful for deducing the structures of organic molecules, but it is more convenient to use simpler representations—structural or graphic formulas—in which a line is used to denote a shared pair of electrons. Because each pair of electrons shared between two atoms is equivalent to a total bond order of 1, each shared pair can be represented by a line between the symbols of the elements. Unshared electrons on the atoms are usually not shown in this kind of representation. The resulting representations of molecules are called graphic formulas or structural formulas. The structural formulas for the compounds (a) to (e) described in Example 21.1 may be written as follows ... 

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. 

A structural formula uses lines between atoms to indicate the covalent bonds. Thus, the two carbon atoms in ethyl alcohol are covalently bonded to each other, the oxygen atom is bonded to one of the carbon atoms, and the six hydrogen atoms are distributed three to one carbon, two to the other carbon, and one to the oxygen. 

Propane, C3Hg, has a structure in which the three carbon atoms are bonded in a row, each end carbon is bonded to three hydrogens, and the middle carbon is bonded to two hydrogens. Draw the structural formula, using lines between atoms to represent covalent bonds. 

The structural language of organic chemistry has been developed so that complex molecules can be described in a clear, yet economical way. A molecule as complex as cholesterol can be drawn rapidly in a bond-line formula, while drawing even a condensed formula would require a prohibitive amount of time. 

Section 1.9 Condensed formulas and bond-line formulas (skeletal diagrams) are used to economize the drawing of organic structures. 

As you become more familiar with organic molecules, you will find bond-line formulas to be very useful tools for representing structures. 

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. 

A dash structural formula has lines that show bonding electron pairs and includes elemental symbols for the atoms in a molecule. 

These formulas are often called Lewis structures in writing them we show all of the valence electrons. Unshared electron pairs are shown as dots, and in dash structural formulas, bonding electron pairs are shown as lines. 

A structural formula uses lines to represent chemical bonds and shows how the atoms in a molecule are connected to each other. The structural formula for hydrogen peroxide is H—O—O—H. In addition to formulas, we also use molecular models—fhree-dimensional representations of molecules—to represent compounds. In fhis book, we use two types of molecular models balTand-stick and space-filling. In ball-and-stick models, we represent atoms as balls and chemical bonds as sticks. The balls and sticks are connected to represent the molecule s shape. The balls are color coded, and each element is assigned a color as shown in the margin. 

We can also represent molecules with structural formulas. The structural formula shows not only the elemental composition, but also the general arrangement of atoms within the molecule. In the case of water, each of the hydrogen atoms is connected to the oxygen atom. Figure 2.13 shows the molecular formula, structural formula, and molecular models (both ball-and-stick and spacefilling variety) for water. Note that the chemical bond between two atoms can be represented with either a pair of dots or a line. 

FIGURE 14.11 The names, formulas, condensed structures, and bond line structures of n-butane and isobutane. These two compounds are isomers since they have the same formula but different structures. A practical use of n-butane is also given. 

FIGURE 20.4 Representation of organic structural formulas with lines the structural formulas showing atoms are on the left and the corresponding line formulas on the right. Each line corner and end represents a carbon atom unless otherwise specified. Each C atom has four covalent bonds or equivalent attached, and the presence of H atoms is implied to provide the required bonds. 

A structural formula uses lines to represent covalent bonds and shows how atoms in a molecule are connected or bonded to each other. The structural formula for H2O2 is ... 

A final point You could have derived the first resonance structure much more quickly hy considering the information given in the reaction scheme leading to the dianion. Thus, the bond-line formula of propyne represents its Lewis structure and the process of removing a proton each from the respective terminal carbons leaves these carbons with two lone electron pairs and the associated charges ... 

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

Convert the following bond-line formulas into Kekul (straight-line) structures. 

Redraw the structures depicted in Problems 39 and 42 using bond-line formulas. 

Suggest a structure for a substance that, upon ozonolysis followed by treatment with (CH3)2S, gives as the sole product CH3COCH2CH2CH2CH2CHO. (Hint Begin by writing out a bond-line formula of this product so that you can clearly see its structure and number its carbon atoms.)... 

Convert the following molecular formulas into line-bond structures that are consistent with valence rules ... 

Identify the functional groups in the following model of arecoiine, a veterinary drug used to control worms in animals. Convert the drawing into a line-bond structure and a molecular formula (red = O, blue = N). 

It appears here with all of the hydrogens showing. In pictures of the structural formulas in organic chemistry, carbon atoms and hydrogen atoms typically aren t shown because the picture would just be too crowded. A carbon atom is implied whenever a line ends or whenever one line joins another. Hydrogens are assumed to connect to any carbon that has a free bond. (Carbon can form four bonds, so if only three are showing, the other is attached to a hydrogen.)... 

Each line in a structural formula represents one pair of shared electrons, but atoms can share more than one pair of electrons. When two atoms share one pair of electrons, the bond is called a single bond, and the structural formula shows a single line. When two atoms share four electrons, the bond is called a double bond, and the structural formula shows two lines between the atoms. Similarly, when two atoms share six electrons, the bond is called a triple bond, and the stmctural formula shows three lines between the atoms. Two carbon atoms can bond to each other through any of these three kinds of bonds, as the compounds in Figure illustrate. 

The first two guidelines state that bonds are represented by lines and that all C—bonds are ignored. Thus we remove the C—H bonds from the structural formula, leaving a bond framework. According to the third guideline, the double bonds remain as two lines ... 

Keep in mind that carbon atoms are not shown in a line structure, so the first step in constructing a structural formula from a line structure is to place a C at every line intersection and at the end of eveiy line. Then add singly bonded hydrogen atoms (—H) until every carbon atom has four bonds. Example 3-3 illustrates this procedure. 

Line drawings show all structural features except carbon atoms and C—H bonds. Convert a line drawing into a structural formula in two steps. Eirst, place a C at any unlabeled line end and at each line... 

While Lavoisier had established a rational system for naming elements and compounds, Frankland developed the system that we use today for writing chemical formulas and for depicting the bonds between the atoms in molecules. As Frankland synthesized more and more isomers, compounds with the same formulas but different molecular structures, he found traditional formulas confusing they showed the types and numbers of elements but provided no clue as to how the atoms were arranged inside the molecule. To remedy the problem, Frankland depicted the atoms in functional groups and drew lines between them to indicate the bonds between the elements. 

Structural formulas also provide information on the way the atoms are arranged and bonded to one another within a molecule. The structural formula of substances not only specifies the type of atoms and how many atoms of each type there are in the molecule of a compound it also provides an outline of the structure of the molecule, pinpointing exactly where each atom is located. Each element in a structural formula is represented by its symbol, and the bonds between atoms are indicated by lines connecting the symbols (see Fig. 60). Thus, structural formulas not only provide information on the type and number of atoms in a molecule of a substance but also depict the internal structure of the molecule of the substance. 

For even more convenience in representing the structures of organic compounds, particularly in printed material, line formulas are used, so-called because they are printed on one line. In line formulas, each carbon atom is written on a line adjacent to the symbols for the other elements to which it is bonded. Line formulas show the general sequence in which the carbon atoms are attached, but in order to interpret them properly, the permitted total bond orders of all the respective atoms must be kept in mind. Again referring to the compounds (a) to (e) described above, the line formulas are as follows ... 

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