Introduction to Organic Chemistry PDF

Introduction to Organic Chemistry  Organic chemistry was singled out as a separate discipline for historical reasons. Originally, it was thought that compounds in living things, termed organic compounds, were fundamentally different from those in nonliving things, called inorganic comp...

Introduction to Organic Chemistry  Organic chemistry was singled out as a separate discipline for historical reasons. Originally, it was thought that compounds in living things, termed organic compounds, were fundamentally different from those in nonliving things, called inorganic compounds. Although we have known for more than 150 years that this distinction is artificial, the name organic persists. Today the term refers to the study of the compounds that contain carbon, many of which, incidentally, are found in living organisms. It may seem odd that a whole discipline is devoted to the study of a single element in the periodic table, when more than 100 elements exist. It turns out, though, that there are far more organic compounds than any other type. Organic chemicals affect virtually every facet of our lives, and for this reason, it is important and useful to know something about them. Clothes, foods, medicines, gasoline, refrigerants, and soaps are composed almost solely of organic molecules. Some, like cotton, wool, or silk are naturally occurring; that is, they can be isolated directly from natural sources. Others, such as nylon and polyester, are synthetic, meaning they are produced by chemists in the laboratory. By studying the principles and concepts of organic chemistry, you can learn more about compounds such as these and how they affect the world around you.  Realize, too, what organic chemistry has done for us. Organic chemistry has made available both comforts and necessities that were previously nonexistent, or reserved for only the wealthy. We have seen an enormous increase in life span, from 47 years in 1900 to over 70 years currently. To a large extent this is due to the isolation and synthesis of new drugs to fight infections and the availability of vaccines for childhood diseases. Chemistry has also given us the tools to control insect populations that spread disease, and there is more food for all because of fertilizers, pesticides, and herbicides. Our lives would be vastly different today without the many products that result from organic chemistry Some Representative Organic Molecules Perhaps the best way to appreciate the variety of organic molecules is to look at a few. Three simple organic compounds are methane, ethanol, and trichlorofluoromethane. Methane, the simplest of all organic compounds, contains one carbon atom. Methane—the main component of natural gas—occurs widely in nature. Like other hydrocarbons—organic compounds that contain only carbon and hydrogen— methane is combustible; that is, it burns in the presence of oxygen. Methane is the product of the anaerobic (without air) decomposition of organic matter by bacteria. The natural gas we use today was formed by the decomposition of organic material millions of years ago. Ethanol, the alcohol present in beer, wine, and other alcoholic beverages, is formed by the fermentation of sugar, quite possibly the oldest example of organic synthesis. Ethanol can also be made in the lab by a totally different process, but the ethanol produced in the lab is identical to the ethanol produced by fermentation WELCOME TO THE WORLD OF ORGANIC CHEMISTRY! In this course, we have seen a variety of molecules that have diverse structures. They represent a miniscule fraction of the organic compounds currently known and the many thousands that are newly discovered or synthesized each year. The principles you learn in organic chemistry will apply to all of these molecules, from simple ones like methane and ethanol, to complex ones like capsaicin and ginkgolide B. It is these beautiful molecules, their properties, and their reactions that we will study in organic chemistry. The Importance of Lewis Structures A properly drawn Lewis structure shows the number of bonds and lone pairs present around each atom in a molecule. In a valid Lewis structure, each H has two electrons, and each second-row element has no more than eight. This is the first step needed to determine many properties of a molecule.  Geometry and Hybridization The number of groups around an atom determines both its geometry and hybridization. Drawing Organic Molecules Shorthand methods are used to abbreviate the structure of organic molecules. Practice Questions IMPORTANCE OF FUNCTIONAL GROUPS The importance of a functional group cannot be overstated. A functional group determines all the following properties of a molecule: bonding and shape type and strength of intermolecular forces physical properties nomenclature chemical reactivity  Intermolecular forces Intermolecular forces are the interactions that exist between molecules. A functional group determines the type and strength of these interactions. Intermolecular forces are also referred to as noncovalent interactions or nonbonded interactions. These are the forces of attraction or repulsion which act between neighboring particles (atoms, molecules or ions). These forces are weak unlike the intramolecular forces, such as covalent bonds between atoms in molecule or ionic bonds between atoms in an ionic compound. Ionic compounds Ionic compounds contain oppositely charged particles held together by extremely strong electrostatic interactions. These ionic interactions are much stronger than the intermolecular forces present between covalent molecules, so it takes a great deal of energy to separate oppositely charged ions from each other. Surface Area  Covalent Compounds Covalent compounds are composed of discrete molecules. The nature of the forces between the molecules depends on the functional group present. There are three different types of interactions, presented here in order of increasing strength: van der Waals forces dipole–dipole interactions hydrogen bonding Van der Waals Forces Van der Waals forces, also called London forces, are very weak interactions caused by the momentary changes in electron density in a molecule. Van der Waals forces are the only attractive forces present in nonpolar compounds. Nonpolar compounds are compounds with symmetrical distribution of charges, where by all the sides around the central atom are identical bonded to the same element with no unshared pairs of electrons, eg. CH4, O2 etc. In simple terms, these are weak electrostatic forces that attract neutral molecules to one another. Dipole–Dipole Interactions Dipole–dipole interactions are the attractive forces between the permanent dipoles of two polar molecules. In acetone, for example, the dipoles in adjacent molecules align so that the partial positive and partial negative charges are in close proximity. These attractive forces caused by permanent dipoles are much stronger than weak van der Waals forces. These interactions are electrostatic interactions between the permanent dipoles of different molecules, they align the molecules to increase the attraction. Dipole: this describes the partial charge separation that can occur within a molecule along the bond that forms between two different atoms. Polar: a polar molecule is one that has uneven charge distribution  Hydrogen Bonding Hydrogen bonding typically occurs when a hydrogen atom bonded to O, N, or F, is electrostatically attracted to a lone pair of electrons on an O, N, or F atom in another molecule. Thus, H2O molecules can hydrogen bond to each other. When they do, a Hydrogen atom covalently bonded to O in one water molecule is attracted to a lone pair of electrons on the O in another water molecule. Hydrogen bonds are the strongest of the three types of intermolecular forces, though they are still much weaker than any covalent bond. Summary of types of Intermolecular forces Boiling Point (bp) The boiling point of a compound is the temperature at which a liquid is converted to a gas. In boiling, energy is needed to overcome the attractive forces in the more ordered liquid state. The stronger the intermolecular forces, the higher the boiling point  Because ionic compounds are held together by extremely strong interactions, they have very high boiling points. The boiling point of NaCl, for example, is 1413 °C. With covalent molecules, the boiling point depends on the identity of the functional group. For compounds of approximately the same molecular weight: Because surface area and polarizability affect the strength of intermolecular forces, they also affect the boiling point. For two compounds with similar functional groups: The larger the surface area, the higher the boiling point. The more polarizable the atoms, the higher the boiling point.  Melting Point (mp) The melting point is the temperature at which a solid is converted to its liquid phase. In melting, energy is needed to overcome the attractive forces in the more ordered crystalline solid. Two factors determine the melting point of a compound: The stronger the intermolecular forces, the higher the melting point. Given the same functional group, the more symmetrical the compound, the higher the melting point. Because ionic compounds are held together by extremely strong interactions, they have very high melting points. For example, the melting point of NaCl is 801 °C. With covalent molecules, the melting point once again depends on the identity of the functional group. For compounds of approximately the same molecular weight.  The C=O bonds in acetone forms hydrogen bond when dissolved in water Butane dissolves in It dissolves in CCl4 CCl4 because they because it are both non-polar contains non-polar organic methyl groups compounds  Because butane and acetone are both organic compounds having a C–C and C– H backbone, they are soluble in the organic solvent CCl4. Butane, a nonpolar molecule, is insoluble in the polar solvent H2O. Acetone, however, is H2O soluble because it contains only three C atoms and its O atom can hydrogen bond with one H atom of H2O. In fact, acetone is so soluble in water that acetone and water are miscible—they form solutions in all proportions with each other. The size of an organic molecule with a polar functional group determines its water solubility. A low molecular weight alcohol like ethanol is water soluble because it has a small carbon skeleton (≤ five C atoms) compared to the size of its polar OH group. Cholesterol, on the other hand, has 27 carbon atoms and only one OH group. Its carbon skeleton is too large for the OH group to solubilize by hydrogen bonding, so cholesterol is insoluble in water. For an organic compound with one functional group, a compound is water soluble only if it has less than five C atoms and contains an O or N atom. SUMMARY OF SOLUBILITY