Solomons Química Orgânica (Inglês) 10th study guide

Solomons Química Orgânica (Inglês) 10th study guide

(Parte 1 de 5)

T. W. GRAHAM SOLOMONS University of South Florida

CRAIG B. FRYHLE Pacific

ROBERT G. JOHNSON Xavier University

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Copyright e 201 1,2008 John Wiley & Sons, Inc. All rights reserved.

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Library of Congress Cataloging-ill-Publication Data

Main Text Solomons, T. W. Graham

Organic ChemistrylT. W. Grabam Solomons.-lOth ed./Craig B. Fryhle. p.cm

Includes index.

ISBN 978-0-470-40141-5 (cloth) Binder-ready version lSBN 978-0-470-55659-7

I. Chemistry, Organic-Textbooks. I. FryWe, Craig B. 1. Title.

QD253.2.S652011 547--{)c22

Study Guide and Solutions Manual ISBN 978-0-470-47839-4

Printed in the United States of America

To the Student

Contrary to what you may have heard, organic chemisty does not have to be a difficult course. It will be a rigorous course, and it will offer a chal lenge. But you will learn more in it than in almost any course you will take--and what you learn will have a special relevance to I ife and the world around you. However, because organic chemistry be ap proached in a logical and systematic way, you will find that with the right study habits, mastering or ganic chemistry be a deeply satisfying experi ence. Here, then, are some suggestions about how to study:

1. Keep UI' with your work from day to day-never let yourself get behind. Organic chemistry is a course in which one idea almost always builds on another that has gone before. It is essential, there fore, that you keep up with, or better yet, be a little abead of your instructor. Ideally, you should try to stay one day ahead of your instructor's lectures in your own class preparations. The lecture, then, will be much more helpful because you will al ready have some understanding of the assigned material. Your time in class will clarify and ex pand ideas that are already familiar ones.

2. Study material in small units, and be sure that you understand each new section before you go on to the next. Again, because of the cumulative nature of organic chemistry, your studying will be much more effective if you take each new idea as it comes and try to understand it completely before you move on to the next concept.

3. Work all of the in-chapter and assigned prob lems. One way to check your progress is to work each of the in-chapter problems when you come to it. These problems have been written just for this purpose and are designed to help you decide whether or not you understand the material that has just been explained. You should also care fully study the Solved Problems. If you under stand a Solved Problem and can work the related in-chapter problem, then you should go on; if you cannot, then you should go back and study the preceding material again. Work all of the prob lems assigned by your instructor from the end of the chapter, as well. Do all of your problems in a notebook and bring this book with you when you go to see your instructor for extra help.

4. Write when you study. Write the reactions, mechanisms, structures, and so on, over and over again. Organic chemistry is best assimilated through the fingertips by writing, and not through the eyes by simply looking, or by higWighting material in the text, or by referring to flash cards.

There is a good reason for this. Organic struc tures, mechanisms, and reactions are complex. If you simply examine them, you may think you un derstand them thoroughly, but that will be a mis perception. The reaction mechanism may make sense to you in a certain way, but you need a deeper understanding than this. You need to know the material so thorougWy that you can explain it to someone else. This level of understanding comes to most of us (those of without photo graphic memories) through writing. Only by writ ing the reaction mechanisms do we pay sufficient attention to their details, such as which atoms are connected to which atoms, which bonds break in a reaction and which bonds form, and the three dimensional aspects of the structures. When we write reactions and mechanisms, connections are made in our brains that provide the long-term memory needed for success in organic chem istry. We virtually guarantee that your grade in the course will be directly proportional to the number of pages of paper that you fill with your own writing in studying during the term.

S. Learn by teaching and explaining. Study with your student peers and practice explaining con cepts and mechanisms to each other. Use the Leaming Group Problems and other exercises your instructor may assign as vehicles for teaching and learning interactively with your peers.

vi TO THE STUDENT

6. Use the answers to the problems ill the Study

Guide in the proper way. Refer to the answers only in two circlllllStances: (I) When YOIl have finished a problem, lise the Study Gllide to check your answer. (2) When, after making a real effort to solve the problem, you find that YOIl are com· pletely stuck, then look at the 3DS\ver for a clue and go back to work out the problem on YOllr own.

The value ofa problem is in solving it. If you sim ply read the problem and look up the answer, you will deprive yourself of an important way to learn.

7. Use molecular models when YOII study. Because of the three-dimensional nature of most organic molecules, molecular models can be an invaluable aid to your understanding ofthem. When you need to see the three-dimensional aspect of a particular topic, use the Molecular Visions TM model set that may have been packaged with your textbook, or bllY a set of models separately. An appendix to the Study Gllide that accompanies this text provides a set of highly useful molecular model exercises.

8. Make lise ofthe rich online teaching resources in WileyPLUS (w.wileypllls.com) and do any online exercises that may be assigned by your in structor.

"Solving the Puzzle" or "Structure Is Everything (Almost)"

Ai> you begin your study of organic chemistry it may seem like a puzzling subject. In fact, in many ways organic chemistry is like a puzzle--a jigsaw puzzle. But it is a jigsaw puzzle with useful pieces, and a puzzle with fewer pieces than perhaps you first thought. In order to put a jigsaw puzzle together you must consider the shape ofthe pieces and how one piece fits together with another. In other words, solving ajigsaw puzzle is about structure. In organic chemistry, molecules are the pieces of the puzzle. Much of organic chemistry, indeed life itself, depends upon the fit of one molecular puzzle piece with another. For example, when an antibody of our immune system acts upon a foreign substance, it is the puzzle-piece-like fit of the antibody with the invading molecule that allows "capture" of the foreign substance. When we smell the sweet scent of a rose, some of the neural impulses are initiated by the fit of a molecule called geraniol in an olfactory receptor site in our nose. When an adhesive binds two surfaces together, it does so by billions of interactions between the molecules of the two materials. Chemistry is truly a captivating subject. As you make the transition from your study of general to organic chemistry, it is impor tant that you solidify those concepts that will help you understand the structure of organic molecules. A number of concepts are discussed below using several examples. It is sug gested that you consider the examples and the explanations given, and refer to information from your general chemistry studies when you need more elaborate information. There are also occasional references below to sections in your text, Solomons and Fryhle's Organic Chemistry, because some of what follows foreshadows what you willieam in the course.

What do we need to know to understand the structure of organic molecules? First, we need to know where electrons are located around a given atom. To understand this we need to recall from general chemistry the ideas of electron configuratiou and valence shell electron orbitals, especially in the case of atoms such as carbon, hydrogen, oxygen, and nitrogen.

We also need to use Lewis valence shell electron structures. These concepts are useful because the shape of a molecule is defined by its constituent atoms, and the placement of the atoms follows from the location of the electrons that bond the atoms. Once have a Lewis structure for a molecule, we can consider orbital hybridization and valence shell electron pair repulsion (VSEPR) theory in order to generate a three-dimensional image of the molecule.

Secondly, in order to understand why specific organic molecular puzzle pieces fittogether we need to consider the attractive and repulsive forces between them. To understand this we need to know how electronic charge is distributed in a molecule. We must use tools such as formal charge and electronegativity. That is, we need to know which parts of a molecule vii viii INTRODUCTION are relatively positive and which are relatively negative-in other words, their polarity.

Associations between molecules strongly depend on both shape and the complementarity of their electrostatic charges (polarity).

When it comes to organic chemistry it will be much easier for you to understand why organic molecules have certain properties and react the way they do if you have an appreci ation for the structnre of the molecules involved. Structure is, in fact, almost everything, in that whenever we want to know why or how something works we look ever more deeply into its structure. This is true whether we are considering a toaster, jet engine, or an organic re action. lfyou can visualize the shape of the puzzle pieces in organic chemistry (molecules), you will see more easily how they fit together (react).

In order to review some of the concepts that will help us understand the structure of organic molecules, let's consider three very important molecules-water, methane, and methanol (methyl alcohol). These three are small and relatively simple molecules that have certain similarities among them, yet distinct differences that be understood on the basis of their structures. Water is a liquid with a moderately high boiling point that does not dissolve organic compounds well. Methanol is also a liquid, with a lower boiling point than water, but one that dissolves many organic compounds easily. Methane is a gas, having a boiling point well below room temperatnre. Water and methanol will dissolve in each other, that is, they are miscible. We shall study the structures of water, methanol, and methane because the principles we learn with these compounds be extended to much larger molecules.

Water HOH

Let's consider the structure of water, beginning with the central oxygen atom. Recall that the atomic number (the number of protons) for oxygen is eight. Therefore, an oxygen atom also has eight electrons. (An ion may have more or less electrons than the atomic number for the element, depending on the charge of the ion.) Only the valence (outermost) shell electrons are involved in bonding. Oxygen bas six valence electrons--that is, six electrons in the second principal shell. (Recall that the number of valence electrons is apparent from the group number of the element in the periodic table, and the row number for the element is the principal shell number for its valence electrons.) Now, let's consider the electron configuration for oxygen. The sequence of atomic orbitals for the first three shells of any atom is shown below. Oxygen uses only the first two shells in its lowest energy state.

The p orbitals of any given principal shell (second, third, etc.) are of equal energy. Recall also that each orbital can hold a maximum of two electrons and that each equal energy orbital must accept one electron before a second reside there (Hund's rule). So, for oxygen we place two electrons in the Is orbital, two in the 2. orbital, and one in each of the

2p orbitals, for a subtotal of seven electrons. The final eighth electron is paired with another in one of the 2p orbitals. The configuration for the eight electrons of oxygen is, therefore

I? 2.2 2Px21pyl 1p,1

INTRODUCTION ix where the superscript numbers indicate how many electrons are in each orbital. In terms of relative energy of these orbitals, the following diagram be drawn. Note that the three 2p orbitals are depicted at the same relative energy level.

JL 2s

JL Is

Energy

Now, let's consider the shape of these orbitals. The shape of an orbital is that of a sphere with the nucleus at the center. The shape of each p orbital is approximately that of a dumbbell or lobe-shaped object, with the nucleus directly between the two lobes. There is one pair of lobes for each of the three p orbitals (Px. Py, Pd and they are aligned along the y, and coordinate axes, with the nucleus at the origin. Note that this implies that the three P orbitals are at 90" angles to each other.

z an orbital Px, Py, Pz orbitals

Now, when oxygen is bonded to two hydrogens, bonding is accomplished by the sharing of an electron from each of the hydrogens with an unpaired electron from the oxygen. This type of bond, involving the sharing of electrons between atoms, is called a covalent bOlld.

The formation of covalent bonds between the oxygen atom and the t:\'{O hydrogen atoms is advantageous because each atom achieves a full valence shell by the sharing of these electrons. For the oxygen in a water molecule, this amounts to satisfying the octet rule.

A Lewis structure for the water molecule (which shows only the valence shell electrons) is depicted in the following structure. There are t:\'{O nonbonding pairs of electrons around the oxygen well as two bonding pairs.

.. '0-. H H x INTRODUCTION

I n the left-hand structure the six valence electrons contributed by the oxygen are shown as dots, while those from the hydrogens are shown as x's. This is done strictly for bookkeeping purposes. All electrons are, of course, identical. The right-hand structure uses the convention that a bonding pair of electrons can be shown by a single line bet.ween the bonded at.oms. This structural model for water is only afirst approximation, however. While it is a proper

(Parte 1 de 5)

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