Introduction and Review GOALS FOR CHAPTER Review concepts from general chemistry that are essen- 自Dawamdntepetheteenotidgoe6aead stry,suc structural formulas and linegomulas types of bonding.electronegativity.and formal charges. Identify acids,bases.electrophiles,and nucleophiles Predict patterns of covalent and ionic bonding involv ng C.H.O,N.and the halogens.Identify resonance- compare the re tive importance 1.1 whe modem detnition of organic chemistry is the chemistry of carbon compounds, ds?u that a w ts com The Origins of an be Organic Chemistry up to form an endless variety of molecules.It is this diversity of carbon compounds rohoror genetic functio plex organic compo serve str ally the isms and their natural products.Compounds such as sugar,urea,starch,waxes,and people accepted Vitalism,the belief that nat I products nee to create them nd mp rals.and In the century.experiments showed that organic compounds could be syn- thesized from inorganic compounds.In 1828,the German chemist Friedrich Wohler The a00 NH:-OCN heat H,N- C-NH 2 and the valves and inne bladder arepolyurethane
px py px pz py pz The modern definition of organic chemistry is the chemistry of carbon compounds. What is so special about carbon that a whole branch of chemistry is devoted to its compounds? Unlike most other elements, carbon forms strong bonds to other carbon atoms and to a wide variety of other elements. Chains and rings of carbon atoms can be built up to form an endless variety of molecules. It is this diversity of carbon compounds that provides the basis for life on Earth. Living creatures are composed largely of complex organic compounds that serve structural, chemical, or genetic functions. The term organic literally means “derived from living organisms.” Originally, the science of organic chemistry was the study of compounds extracted from living organisms and their natural products. Compounds such as sugar, urea, starch, waxes, and plant oils were considered “organic,” and people accepted Vitalism, the belief that natural products needed a “vital force” to create them. Organic chemistry, then, was the study of compounds having the vital force. Inorganic chemistry was the study of gases, rocks, and minerals, and the compounds that could be made from them. In the nineteenth century, experiments showed that organic compounds could be synthesized from inorganic compounds. In 1828, the German chemist Friedrich Wöhler converted ammonium cyanate, made from ammonia and cyanic acid, to urea simply by heating it in the absence of oxygen. 1 GOALS FOR CHAPTER 1 1Introduction and Review 1-1 The Origins of Organic Chemistry Review concepts from general chemistry that are essential for success in organic chemistry, such as the electronic structure of the atom, Lewis structures and the octet rule, types of bonding, electronegativity, and formal charges. Predict patterns of covalent and ionic bonding involving C, H, O, N, and the halogens. Identify resonancestabilized structures and compare the relative importance of their resonance forms. Draw and interpret the types of structural formulas commonly used in organic chemistry, including condensed structural formulas and line–angle formulas. Identify acids, bases, electrophiles, and nucleophiles. Compare their strengths and predict their reactions based on structure and bonding, as well as and values. Ka pKa The AbioCor self-contained artificial heart, which was first implanted into a patient on July 3, 2001. The outer shell is polycarbonate, and the valves and inner bladder are polyurethane. NH4 + −OCN heat 2N CH NH2 O urea (organic) ammonium cyanate (inorganic)
2 CHAPTER 1 Introduction and Review Urea had always come from living organisms and wa sumed to contain the vital force.vet ammonium cyanate is inorganic and thus lacks the vital force.Some chemists claimed that a trace of vital force from Wohler's hands must have contaminated the reaction. ny other syntheses were carred Since Vitalism was disproved in the early nineteenth century,you'd think it would be extinct by now.And you'd be wrong!Vitalism lives on today in the minds of those plant-denved) vitamins.lavor comp more ne nds min th re the c way to tell the art is th radioactive 4C and appear old because their 4C has decayed over time.Plant-derived compounds are recently synthesized from CO2 in the air.They have a higher content of large chemical suppliers provide isotope-ratio analyses to show that their "naturals"have high C content and are plant-derived.Such a sophisticated aalysisdi-c favor ury form of Vitalism guished fom nds.The distinctive featur ounds is that they a contain one or more carbon atoms.Still.not all carbon compounds are organic substances such as diamond.graphite.carbon dioxide.ammonium cyanate.and sodium carbonate are derived from minerals and ave typical inorganic properties.Most of the chemical in the brain's reward system. ely of we are nourished by the organic compounds in our food.The prot ins in our skin the linids in our cell mem branes,the glycogen in our livers,and the DNA in the nuclei of our cells are all organic compounds.Our bodies are also regulated and defended by complex organic compounds armin OH COOH HO HO OH Four examples of organic compounds in living organisms.Tobacco conains nicotine.an addictive alkaloid.Rose hips contain Pain-rclevi
glucose OH OH COOH OH O O HO carmine Application: Biochemistry One of nicotine’s effects is to increase the concentration of dopamine, a chemical in the brain’s reward system. Release of this chemical makes smokers feel good and reinforces the need to smoke. 2 CHAPTER 1 Introduction and Review Urea had always come from living organisms and was presumed to contain the vital force, yet ammonium cyanate is inorganic and thus lacks the vital force. Some chemists claimed that a trace of vital force from Wöhler’s hands must have contaminated the reaction, but most recognized the possibility of synthesizing organic compounds from inorganics. Many other syntheses were carried out, and the vital force theory was eventually discarded. Since Vitalism was disproved in the early nineteenth century, you’d think it would be extinct by now. And you’d be wrong! Vitalism lives on today in the minds of those who believe that “natural” (plant-derived) vitamins, flavor compounds, etc. are somehow different and more healthful than the identical “artificial” (synthesized) compounds. As chemists, we know that plant-derived compounds and the synthesized compounds are identical. Assuming they are pure, the only way to tell them apart is through dating: Compounds synthesized from petrochemicals have a lower content of radioactive and appear old because their has decayed over time. Plant-derived compounds are recently synthesized from in the air. They have a higher content of radioactive Some large chemical suppliers provide isotope-ratio analyses to show that their “naturals” have high content and are plant-derived. Such a sophisticated analysis lends a high-tech flavor to this twenty-first-century form of Vitalism. Even though organic compounds do not need a vital force, they are still distinguished from inorganic compounds. The distinctive feature of organic compounds is that they all contain one or more carbon atoms. Still, not all carbon compounds are organic; substances such as diamond, graphite, carbon dioxide, ammonium cyanate, and sodium carbonate are derived from minerals and have typical inorganic properties. Most of the millions of carbon compounds are classified as organic, however. We humans are composed largely of organic molecules, and we are nourished by the organic compounds in our food. The proteins in our skin, the lipids in our cell membranes, the glycogen in our livers, and the DNA in the nuclei of our cells are all organic compounds. Our bodies are also regulated and defended by complex organic compounds. 14C 14C. CO2 14C 14C 14C N N CH3 nicotine Four examples of organic compounds in living organisms. Tobacco contains nicotine, an addictive alkaloid. Rose hips contain vitamin C, essential for preventing scurvy. The red dye carmine comes from cochineal insects, shown on a prickly pear cactus. Opium poppies contain morphine, a pain-relieving, addictive alkaloid. OH O CH2OH HO HCOH H O vitamin C morphine O OH OH H N CH3
1-2 Principles of Atomic Structure 3 The s Many of the most important advances in medicine are actually advances in organic derivatives of complex organic com. chemistry.New synthetic drugs are developed to combat disease,and new polymers pounds like morphine is to discover new ugs that reta ogans.and now it gives us the drugs and in the propertieshighlMyadicivel +1-2 Before we begin our study of organic chemistry,we must review some basic princi- ples.These concepts of atomic and molecular structure are crucial to your understand- Principles of Atomic ing of the structure and bonding of organic compounds. Structure 1-2A Structure of the Atom e nchan)e co Atoms are made up of p ons neutrons and electrons Protons ar Ineutrons have simila cloud of ele but it is the oms mass is in the Each element is distinguished by the number of protons in the nucleus (the atomic number).The number of neutrons is usually similar to the number of protons,although the number of neutrons may vary.Atoms with the same number of protons but dif are cand six common sum of the protons and neutrons)is 12.and we write its symbol as C.About 1%of (protons and neutrons) carbon atoms have seven neutrons:the mass number is 13,written13 fraction of bn toms have mass number of 14.The structure.An atom ha a dense.positively charged nucleus materials up to about 50.000 vears old. surrounded by a cloud of electrons. 1-28 Electronic Structure of the Atom ties are e determined by the number of protons in the nuc of the light,electrons show properties of both particles and waves;in many ways,the electrons lectro are are Io nd i or s use to that oms and where the electron is:nevertheless,we can determine the electron density,the proba- bility of finding the electron in a particular part of the orbital.An orbital,then,is an ron,with an associated probability function that defines Atom e1 lo"at d:Ceattn nucleus.Each shell is identified by a principal quantum number n withn=I for the rgy shell closest to the nucleus.Asnreases.the shells Relative orbital energies higher in energy,and can mo re electrons.M of the two rows -2-2g,-2p The first electron shell contains just the Is orbital.All s orbitals are spherically
1-2 Principles of Atomic Structure 3 Chemists have learned to synthesize or simulate many of these complex molecules. The synthetic products serve as drugs, medicines, plastics, pesticides, paints, and fibers. Many of the most important advances in medicine are actually advances in organic chemistry. New synthetic drugs are developed to combat disease, and new polymers are molded to replace failing organs. Organic chemistry has gone full circle. It began as the study of compounds derived from “organs,” and now it gives us the drugs and materials we need to save or replace those organs. 1-2 Principles of Atomic Structure Application: Drug Research One of the reasons chemists synthesize derivatives of complex organic compounds like morphine is to discover new drugs that retain the good properties (potent painrelieving) but not the bad properties (highly addictive). Before we begin our study of organic chemistry, we must review some basic principles. These concepts of atomic and molecular structure are crucial to your understanding of the structure and bonding of organic compounds. 1-2A Structure of the Atom Atoms are made up of protons, neutrons, and electrons. Protons are positively charged and are found together with (uncharged) neutrons in the nucleus. Electrons, which have a negative charge that is equal in magnitude to the positive charge on the proton, occupy the space surrounding the nucleus (Figure 1-1). Protons and neutrons have similar masses, about 1800 times the mass of an electron. Almost all the atom’s mass is in the nucleus, but it is the electrons that take part in chemical bonding and reactions. Each element is distinguished by the number of protons in the nucleus (the atomic number). The number of neutrons is usually similar to the number of protons, although the number of neutrons may vary. Atoms with the same number of protons but different numbers of neutrons are called isotopes. For example, the most common kind of carbon atom has six protons and six neutrons in its nucleus. Its mass number (the sum of the protons and neutrons) is 12, and we write its symbol as About 1% of carbon atoms have seven neutrons; the mass number is 13, written A very small fraction of carbon atoms have eight neutrons and a mass number of 14. The isotope is radioactive, with a half-life (the time it takes for half of the nuclei to decay) of 5730 years. The predictable decay of is used to determine the age of organic materials up to about 50,000 years old. 1-2B Electronic Structure of the Atom An element’s chemical properties are determined by the number of protons in the nucleus and the corresponding number of electrons around the nucleus. The electrons form bonds and determine the structure of the resulting molecules. Because they are small and light, electrons show properties of both particles and waves; in many ways, the electrons in atoms and molecules behave more like waves than like particles. Electrons that are bound to nuclei are found in orbitals. Orbitals are mathematical descriptions that chemists use to explain and predict the properties of atoms and molecules. The Heisenberg uncertainty principle states that we can never determine exactly where the electron is; nevertheless, we can determine the electron density, the probability of finding the electron in a particular part of the orbital. An orbital, then, is an allowed energy state for an electron, with an associated probability function that defines the distribution of electron density in space. Atomic orbitals are grouped into different “shells” at different distances from the nucleus. Each shell is identified by a principal quantum number n, with for the lowest-energy shell closest to the nucleus. As n increases, the shells are farther from the nucleus, higher in energy, and can hold more electrons. Most of the common elements in organic compounds are found in the first two rows of the periodic table, indicating that their electrons are found in the first two electron shells. The first shell can hold two electrons, and the second shell can hold eight. The first electron shell contains just the 1s orbital. All s orbitals are spherically symmetrical, meaning that they are nondirectional. The electron density is only a function of the distance from the nucleus. The electron density of the 1s orbital is graphed 1n = 12 1n = 22 n = 1 14C 14C 13C. 12C. cloud of electrons nucleus (protons and neutrons) + FIGURE 1-1 Basic atomic structure. An atom has a dense, positively charged nucleus surrounded by a cloud of electrons. Relative orbital energies energy 2py 2pz 2px 1s 2s
4 CHAPTER 1 Introduction and Review FIGURE 1-2 Grappl.Th highest at the nucleus and dropsoff electron density direction. distance nucleus and falls off e distance fror ined as a cotton boll,with the cottonseed at the middle representing the nucleus.The density of the cotton is highest nearest the seed,and it becomes less dense at greater sconsasofte2sand2portbiak.Tie2sotilisPhes the Is orbital.but its elect on density is not a simnle e function.The2s orbital has a smaller amount of electron density close to the nucleus Most of the electron density is farther away,beyond a region of zero electron density called a no Becau thes electron density is farther from the ha one oriented ineach of the three spatial directions.These orbitls are called the2pthe 2pand the 2paccording to their direction along they,oraxis.The 2p orbitals electron density od leu nucleus Graph and diagram of the 2s atomic orbital.The s,but mo ctron density ther from the
4 CHAPTER 1 Introduction and Review electron density distance from the nucleus distance 1s nucleus FIGURE 1-2 Graph and diagram of the 1s atomic orbital. The electron density is highest at the nucleus and drops off exponentially with increasing distance from the nucleus in any direction. in Figure 1-2. Notice how the electron density is highest at the nucleus and falls off exponentially with increasing distance from the nucleus. The 1s orbital might be imagined as a cotton boll, with the cottonseed at the middle representing the nucleus. The density of the cotton is highest nearest the seed, and it becomes less dense at greater distances from this “nucleus.” The second electron shell consists of the 2s and 2p orbitals. The 2s orbital is spherically symmetrical like the 1s orbital, but its electron density is not a simple exponential function. The 2s orbital has a smaller amount of electron density close to the nucleus. Most of the electron density is farther away, beyond a region of zero electron density called a node. Because most of the 2s electron density is farther from the nucleus than that of the 1s, the 2s orbital is higher in energy. Figure 1-3 shows a graph of the 2s orbital. In addition to the 2s orbital, the second shell also contains three 2p atomic orbitals, one oriented in each of the three spatial directions. These orbitals are called the the and the according to their direction along the 2p x, y, or z axis. The 2p orbitals z 2p , y, 2px, electron density node node distance from the nucleus distance from the nucleus node node 2s nucleus FIGURE 1-3 Graph and diagram of the 2s atomic orbital. The 2s orbital has a small region of high electron density close to the nucleus, but most of the electron density is farther from the nucleus, beyond a node, or region of zero electron density
1-2 Principles of Atomic Structure 5 angles to each other. orientation aongtheorais directions of axes nucleus (comes out toward us) e 2p orbital at 90"angles are slightly higher in energy than the 2s.because the average location of the electron rfrom the nu .Each p orbita 10 es.one or The three 2 orbitals differ ony in their spatial orientation.so they have identical energies.Orbitals deg degenerate orbitals.Fresho vided that their paired.The first shell (one Is orbital)can ac modate two electrons.The second shell (one 2s orbital and three 2p orbitals)can accom modate eight electrons.and the third shell (one 3s orbital,three 3p orbitals,and five3d orbitals)can accommodate 18 electrons 1-2c Electronic Configurations of Atoms ,and the .we fill the orbitals in order until we have added the ber of elctrons.Table1-I shows the ground-state electronic configurations of the el alt of lithium.is a wo ac concepts are illustrated le 1-1.7 valer e electrons are mood-stbliznn used to treat the n has six.Helium has a filled first shell with two valence psychiatric disorder known as mania. electrons.and neon has has a filled second shell with eight valence electrons(ten elec- Mania is characterized by behaviors ucn as elated mood,lee ngs of the per correspo o t er o A1 lithiumcrbonate helps to stabilize group4A of the periodic table. these patients'moods
1-2 Principles of Atomic Structure 5 are slightly higher in energy than the 2s, because the average location of the electron in a 2p orbital is farther from the nucleus. Each p orbital consists of two lobes, one on either side of the nucleus, with a nodal plane at the nucleus. The nodal plane is a flat (planar) region of space, including the nucleus, with zero electron density. The three 2p orbitals differ only in their spatial orientation, so they have identical energies. Orbitals with identical energies are called degenerate orbitals. Figure 1-4 shows the shapes of the three degenerate 2p atomic orbitals. The Pauli exclusion principle tells us that each orbital can hold a maximum of two electrons, provided that their spins are paired. The first shell (one 1s orbital) can accommodate two electrons. The second shell (one 2s orbital and three 2p orbitals) can accommodate eight electrons, and the third shell (one 3s orbital, three 3p orbitals, and five 3d orbitals) can accommodate 18 electrons. 1-2C Electronic Configurations of Atoms Aufbau means “building up” in German, and the aufbau principle tells us how to build up the electronic configuration of an atom’s ground (most stable) state. Starting with the lowest-energy orbital, we fill the orbitals in order until we have added the proper number of electrons. Table 1-1 shows the ground-state electronic configurations of the elements in the first two rows of the periodic table. Two additional concepts are illustrated in Table 1-1. The valence electrons are those electrons that are in the outermost shell. Carbon has four valence electrons, nitrogen has five, and oxygen has six. Helium has a filled first shell with two valence electrons, and neon has has a filled second shell with eight valence electrons (ten electrons total). In general (for the representative elements), the column or group number of the periodic table corresponds to the number of valence electrons (Figure 1-5). Hydrogen and lithium have one valence electron, and they are both in the first column (group 1A) of the periodic table. Carbon has four valence electrons, and it is in group 4A of the periodic table. nucleus distance from the nucleus electron density node 2p the 2px orbital the 2px, 2py, and 2pz orbitals superimposed at 90° angles x y z directions of axes (z comes out toward us) x y x z y z nodal plane FIGURE 1-4 The 2p orbitals. Three 2p orbitals are oriented at right angles to each other. Each is labeled according to its orientation along the x, y, or z axis. Application: Drugs Lithium carbonate, a salt of lithium, is a mood-stabilizing agent used to treat the psychiatric disorder known as mania. Mania is characterized by behaviors such as elated mood, feelings of greatness, racing thoughts, and an inability to sleep. We don’t know how lithium carbonate helps to stabilize these patients’ moods