## shape and structure of organic compounds

Each carbon atom is understood to be attached to enough hydrogen atoms to give each carbon atom four bonds. Nevertheless, it is useful to compare typical members of each class, as in Table $$\PageIndex{1}$$. With few exceptions, carbon compounds can be formulated with four . Structural units that have $$C-C-C$$ valence angles substantially less than the tetrahedral value include double and triple bonds, and small rings such as cyclopropane. Different compounds having the same molecular formula are called isomers , and the prevalence of organic isomers reflects the extraordinary versatility of carbon in forming strong bonds to itself and to other elements. The customary unit of length is the angstrom$$^1$$ ($$\text{A} = 10^{-10} \: \text{m}$$), and measurements often can be made with an accuracy of $$0.001 \: \text{A}$$ by using the techniques of molecular spectroscopy, x-ray diffraction (for crystalline solids), and electron diffraction (for volatile compounds). organic compounds and begin to see how the practicing organic chemist visu- alizes molecules and correlates the diverse kinds of structures that he has to deal with in his work. Organic Chemistry With a Biological Emphasis by Tim Soderberg (University of Minnesota, Morris). Alkyl groups are not independent molecules; they are parts of molecules that we consider as a unit to name compounds systematically. These effects are apparent in the data of Table 2-1, which lists the bond lengths in several simple organic compounds. To name alkanes by the IUPAC system and write formulas for alkanes given IUPAC names. To describe functional groups and explain why they are useful in the study of organic chemistry. For this reason, ball-and-stick models or their equivalent are more generally useful than the space-filling models for visualizing structures and the positions of the atoms relative to one another. It is well established that the normal carbon atom forms its four single bonds in compounds of the type $$CX_4$$ so that the four attached atoms lie at the corners of a regular tetrahedron. To identify and name simple (straight-chain) alkanes given formulas and write formulas for straight-chain alkanes given their names. The flat representations shown do not accurately portray bond angles or molecular geometry. Whereas methane, $$CH_4$$, is tetrahedral, ethene, $$C_2H_4$$, is not. The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. Watch the recordings here on Youtube! Scientists of the 18th and early 19th centuries studied compounds obtained from plants and animals and labeled them organic because they were isolated from “organized” (living) systems. Models of ethene and methanal can be built with ball-and-stick models by using flexible couplings or bent sticks to form the double bonds (Figure 2-2), but the $$H-C-H$$ angles are inaccurate because they are $$109.5^\text{o}$$ rather than the observed $$117^\text{o}$$ to $$118^\text{o}$$. We use several kinds of formulas to describe organic compounds. Functional groups are atoms or small groups of atoms (two to four) that exhibit a characteristic reactivity. As we noted, there are several different kinds of hydrocarbons. It is necessary to draw structural formulas for organic compounds because in most cases a molecular formula does not uniquely represent a single compound. Methyl groups (rule 2) are attached to the second and fifth carbon atoms. Atoms or groups attached to this carbon chain, called substituents, are then named, with their positions indicated by numbers. • What he expected is described by the following equation. Methane (CH4), ethane (C2H6), and propane (C3H8) are the beginning of a series of compounds in which any two members in a sequence differ by one carbon atom and two hydrogen atoms—namely, a CH2 unit. The lengths of single $$C-C$$ bonds also vary significantly depending on what other atoms or groups are attached to the carbons. My Notes . It would be difficult to assign unique individual names that we could remember. Watch Next Video. • Write condensed structural formulas for alkanes given complete structural formulas. As we noted, there are several different kinds of hydrocarbons. The alkyl groups we will use most frequently are listed in Table $$\PageIndex{4}$$. Organic molecules strongly resist deformation forces that alter their valence angles from normal values. For now, we will consider only those substituents called alkyl groups. In the ball-and-stick type, the sticks usually come in various lengths to simulate different kinds of bonds; $$C-H$$ bonds typically are scaled to represent $$1.1 \: \text{A}$$, $$C-C$$ bonds to be $$1.54 \: \text{A}$$, and $$C=C$$ and $$C \equiv C$$ to be correspondingly shorter. For now, we will only worry about drawing and recognizing each functional group, as depicted by Lewis and line structures. There are 3 pentanes, 5 hexanes, 9 heptanes, and 18 octanes. Today organic chemistry is the study of the chemistry of the carbon compounds, and inorganic chemistry is the study of the chemistry of all other elements. The length of a chemical bond is the average distance between the nuclei of two bonded atoms, regardless of where the bonding electrons happen to be. Using this formula, we can write a molecular formula for any alkane with a given number of carbon atoms. A systematic way of naming hydrocarbons and other organic compounds has been devised by the International Union of Pure and Applied Chemistry (IUPAC).