Chemistry
Naming Cycloalkenes
Naming cycloalkenes involves identifying the parent chain by counting the number of carbon atoms in the cycloalkene ring and using the corresponding prefix (e.g., cyclopropane, cyclopentene). The position of the double bond is indicated by the lowest possible number, and the suffix "-ene" is added to the parent chain name to denote the presence of a double bond.
Written by Perlego with AI-assistance
Related key terms
1 of 5
10 Key excerpts on "Naming Cycloalkenes"
eBook - PDF- T. W. Graham Solomons, Craig B. Fryhle, Scott A. Snyder(Authors)
- 2017(Publication Date)
- Wiley(Publisher)
4.5 HOW TO NAME ALKENES AND CYCLOALKENES 159 4. Number substituted cycloalkenes in the way that gives the carbon atoms of the double bond the 1 and 2 positions and that also gives the substituent groups the lower numbers at the first point of difference. With substituted cycloalkenes it is not neces- sary to specify the position of the double bond since it will always begin with C1 and C2. The two examples shown here illustrate the application of these rules: 3,5-Dimethylcyclohexene (not 4,6-dimethylcyclohexene) 1-Methylcyclopentene (not 2-methylcyclopentene) 3 2 4 5 3 2 5 6 4 1 1 5. Name compounds containing a double bond and an alcohol group as alkenols (or cycloalkenols) and give the alcohol carbon the lower number: OH 3 2 1 OH 2 4 5 3 1 4-Methyl-3-penten-2-ol or 4-methylpent-3-en-2-ol 2-Methyl-2-cyclohexen-1-ol or 2-methylcyclohex-2-en-1-ol 6. Two frequently encountered alkenyl groups are the vinyl group and the allyl group: The allyl group The vinyl group Using substitutive nomenclature, the vinyl and allyl groups are called ethenyl and prop-2-en-1-yl, respectively. The following examples illustrate how these names are employed: Cl 3-Chloropropene or allyl chloride (common) Br Bromoethene or vinyl bromide (common) Ethenylcyclopropane or vinylcyclopropane OH 3-(Prop-2-en-1-yl)cyclohexan-1-ol or 3-allylcyclohexanol 7. If two identical or substantial groups are on the same side of the double bond, the compound can be designated cis; if they are on opposite sides it can be designated trans: Cl Cl Cl Cl trans-1,2-Dichloroethene cis-1,2-Dichloroethene (In Section 7.2 we shall see another method for designating the geometry of the double bond.) 160 CHAPTER 4 NOMENCLATURE AND CONFORMATIONS OF ALKANES AND CYCLOALKANES 4.6 HOW TO NAME ALKYNES Alkynes are named in much the same way as alkenes. Unbranched alkynes, for example, are named by replacing the -ane of the name of the corresponding alkane with the ending -yne.
eBook - PDF- T. W. Graham Solomons, Craig B. Fryhle, Scott A. Snyder(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
4.4 How to Name Cycloalkanes 161 4.4B How To Name Bicyclic Cycloalkanes 1. We name compounds containing two fused or bridged rings as bicycloalkanes, and we use the name of the alkane corresponding to the total number of carbon atoms in the rings as the parent name. The following compound, for example, contains seven carbon atoms and is, therefore, a bicycloheptane. The carbon atoms common to both rings are called bridgeheads, and each bond, or each chain of atoms connecting the bridgehead atoms, is called a bridge. Two- carbon bridge Two- carbon bridge One-carbon bridge Bridgehead Bridgehead C H H C H 2 C H 2 C CH 2 CH 2 CH 2 = = = A bicycloheptane 2. We then interpose an expression in brackets within the name that denotes the number of carbon atoms in each bridge (in order of decreasing length). Fused rings have zero car- bons in their bridge. For example, C H H C H 2 C H 2 C CH 2 CH 2 CH 2 Bridged Bicyclo[2.2.1]heptane (also called norbornane) H 2 C CH 2 C H H C = = Bicyclo[1.1.0]butane Fused 3. In bicycloalkanes with substituents, we number the bridged ring system beginning at one bridgehead, proceeding first along the longest bridge to the other bridgehead, then along the next longest bridge back to the first bridgehead; the shortest bridge is numbered last. 2 4 5 1 6 7 3 8 Bridged 8-Methylbicyclo[3.2.1]octane Fused 8-Methylbicyclo[4.3.0]nonane 7 9 4 3 6 1 2 5 8 HELPFUL HINT Explore the structures of these bicyclic compounds by building hand-held molecular models. Write a structural formula for 7,7-dichlorobicyclo[2.2.1]heptane. Strategy and Answer First we write a bicyclo[2.2.1]heptane ring and number it. Then we add the substituents (two chlorine atoms) to the proper carbon. Cl Cl SOLVED PROBLEM 4.3 162 CHAPTER 4 Nomenclature and Conformations of Alkanes and Cycloalkanes 4.5 How To Name Alkenes and Cycloalkenes The IUPAC rules for naming alkenes are similar in many respects to those for naming alkanes: 1.
eBook - PDF- T. W. Graham Solomons, Craig B. Fryhle, Scott A. Snyder(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
Name compounds containing a double bond and an alcohol group as alkenols (or cycloalkenols) and give the alcohol carbon the lower number: OH 3 2 1 OH 2 4 5 3 1 4-Methyl-3-penten-2-ol or 4-methylpent-3-en-2-ol 2-Methyl-2-cyclohexen-1-ol or 2-methylcyclohex-2-en-1-ol 6. Two frequently encountered alkenyl groups are the vinyl group and the allyl group: The allyl group The vinyl group Using substitutive nomenclature, the vinyl and allyl groups are called ethenyl and prop-2-en-1-yl, respectively. The following examples illustrate how these names are employed: Cl 3-Chloropropene or allyl chloride (common) Br Bromoethene or vinyl bromide (common) Ethenylcyclopropane or vinylcyclopropane OH 3-(Prop-2-en-1-yl)cyclohexan-1-ol or 3-allylcyclohexanol 7. If two identical or substantial groups are on the same side of the double bond, the compound can be designated cis; if they are on opposite sides it can be designated trans: Cl Cl Cl Cl trans-1,2-Dichloroethene cis-1,2-Dichloroethene (In Section 7.2 we shall see another method for designating the geometry of the double bond.) 160 CHAPTER 4 NOMENCLATURE AND CONFORMATIONS OF ALKANES AND CYCLOALKANES • • 4.6 HOW TO NAME ALKYNES Alkynes are named in much the same way as alkenes. Unbranched alkynes, for example, are named by replacing the -ane of the name of the corresponding alkane with the ending -yne. The chain is numbered to give the carbon atoms of the triple bond the lower pos- sible numbers. The lower number of the two carbon atoms of the triple bond is used to designate the location of the triple bond. When double and triple bonds are present, the direction of numbering is chosen so as to give the lowest overall set of locants. In the face of equivalent options, then preference is given to assigning lowest numbers to the double bonds.
eBook - PDF- David R. Klein(Author)
- 2021(Publication Date)
- Wiley(Publisher)
Our discussion of conformational analysis will involve the comparison of many different compounds and will be more efficient if we can refer to compounds by name. A system of rules for naming alkanes and cycloalkanes will be developed prior to our discussion of molecular flexibility. Top (Ribbon) JamesBrey/Getty Images; Bottom Left (Spiral ribbon) macida/Getty Images; Bottom Middle [Left and Right] (Ribbon) JamesBrey/Getty Images; Bottom Right (Spiral ribbon) macida/Getty Images 4.2 Nomenclature of Alkanes 139 4.1 Introduction to Alkanes Recall that hydrocarbons are compounds comprised of only C and H; for example: C C H H H H H H Ethane C 2 H 6 C C H H H H Ethylene C 2 H 4 C C H H Acetylene C 2 H 2 Benzene C 6 H 6 Ethane is unlike the other examples in that it has no π bonds. Hydrocarbons that lack π bonds are called saturated hydrocarbons, or alkanes. The names of these compounds usually end with the suffix “-ane,” as seen in the following examples: Propane Butane Pentane This chapter will focus on alkanes, beginning with a procedure for naming them. The system of nam- ing chemical compounds, or nomenclature, will be developed and refined throughout the remaining chapters of this book. 4.2 Nomenclature of Alkanes An Introduction to IUPAC Nomenclature In the early nineteenth century, organic compounds were often named at the whim of their discov- erers. Here are just a few examples: Formic acid Isolated from ants and named after the Latin word for ant, formica H OH O Urea Isolated from urine H 2 N NH 2 O Barbituric acid Adolf von Baeyer named this compound in honor of a woman named Barbara N N O O O H H Morphine A painkiller named after the Greek god of dreams, Morpheus O HO HO N H A large number of compounds were given names that became part of the common language shared by chemists. Many of these common names are still in use today. As the number of known compounds grew, a pressing need arose for a systematic method for naming compounds.
eBook - PDF- David R. Klein(Author)
- 2020(Publication Date)
- Wiley(Publisher)
The system of nam- ing chemical compounds, or nomenclature, will be developed and refined throughout the remaining chapters of this book. 4.2 NOMENCLATURE OF ALKANES An Introduction to IUPAC Nomenclature In the early nineteenth century, organic compounds were often named at the whim of their discover- ers. Here are just a few examples: Formic acid Isolated from ants and named after the Latin word for ant, formica H OH O Urea Isolated from urine H 2 N NH 2 O Barbituric acid Adolf von Baeyer named this compound in honor of a woman named Barbara N N O O O H H Morphine A painkiller named after the Greek god of dreams, Morpheus O HO HO N H A large number of compounds were given names that became part of the common language shared by chemists. Many of these common names are still in use today. As the number of known compounds grew, a pressing need arose for a systematic method for naming compounds. In 1892, a group of 34 European chemists met in Switzerland and developed a system of organic nomenclature called the Geneva rules. The group ultimately became known as the International Union of Pure and Applied Chemistry, or IUPAC (pronounced “I–YOU–PACK”). The original Geneva rules have been regularly revised and updated and are now called IUPAC nomenclature. DO YOU REMEMBER? Before you go on, be sure you understand the following topics. If necessary, review the suggested sections to prepare for this chapter. • Molecular Orbital Theory (Section 1.8) • Predicting Geometry (Section 1.10) • Bond-Line Structures (Section 2.2) • Three-Dimensional Bond-Line Structures (Section 2.6) 134 CHAPTER 4 Alkanes and Cycloalkanes Names produced by IUPAC rules are called systematic names. There are many rules, and we cannot possibly study all of them. The upcoming sections are meant to serve as an introduction to IUPAC nomenclature.
eBook - PDF- William H. Brown, Thomas Poon(Authors)
- 2017(Publication Date)
- Wiley(Publisher)
If there are two substituents, number the ring by beginning with the substituent of lower alphabetical order. If there are three or more substituents, number the ring so as to give them the lowest set of numbers, and then list the substituents in alphabetical order. Cycloalkane A saturated hydrocarbon that contains carbon atoms joined to form a ring. H 2 C H 2 C CH 2 CH 2 Cyclobutane or Cyclopentane or CH 2 H 2 C H 2 C CH 2 CH 2 CH 2 Cyclohexane or H 2 C CH 2 H 2 C CH 2 CH 2 FIGURE 3.3 Examples of cycloalkanes. P R O B L E M 3.4 Classify each hydrogen atom in the following compounds as 1°, 2°, or 3°. (a) CH 3 CHCH 2 CH 2 CH 3 CH 3 (b) C CH 3 CH 3 CH 3 CH 3 CH 3 CH 2 CH E X A M P L E 3.5 Write the molecular formula and IUPAC name for each cycloalkane. (a) (b) (c) (d) S T R AT E G Y First determine the root name of the cycloalkane. Then name the substituents and place them in alphabetical order. Number the parent chain so as to give the lower number to the substituent encountered first. If substituents have equivalent positions, the lower number is assigned to the substituent with the lower alphabetical order. 3.4 3 . 4 What Are Cycloalkanes? 71 P R O B L E M 3.5 Write the molecular formula and IUPAC name for each cycloalkane: (a) (b) (c) (d) S O L U T I O N (a) The molecular formula of this cycloalkane is C 8 H 16 . Because there is only one substituent on the ring, there is no need to number the atoms of the ring. The IUPAC name of this compound is isopropylcyclopentane. (b) Number the atoms of the cyclohexane ring by beginning with tert‐butyl, the substituent of lower alphabetical order. The compound’s name is 1‐tert‐butyl‐4‐methylcyclohexane, and its molecular formula is C 11 H 22 . (c) The molecular formula of this cycloalkane is C 13 H 26 . The compound’s name is 1‐ethyl‐2‐ isopropyl‐4‐methylcycloheptane. The ethyl group is numbered 1 because this allows the isopropyl group to be encountered sooner than if the methyl group were numbered 1.
eBook - ePubOrganic Chemistry
An Acid-Base Approach, Third Edition
- Michael B. Smith(Author)
- 2022(Publication Date)
- CRC Press(Publisher)
Cyclic alkanes can have substituents attached, and the position of a substituent attached to a cyclic alkane is assigned the lowest possible number. In methylcyclohexane, this six-membered cyclic alkane is a cyclohexane with one methyl substituent. Since there is only one group attached to the ring the 1- is obvious and it is omitted so the name is just methylcyclohexane. With 1,3-dimethylcyclohexane, however, several isomers are possible so both numbers must be included to specify the position of the methyl groups. The ring is numbered from one methyl group to give the lowest possible combination of numbers. It is 1,3-dimethylcyclohexane. If two different substituents are attached to the ring, the names are listed in alphabetical order and the first cited substituent is assigned to C1. An example is 1-ethyl-3-methylcycloheptane. If there are three or more substituents, the rules are slightly different. List the substituents in alphabetical order, but C1 is chosen so the lowest combination of numbers is obtained. An example is 4-chloro-2-ethyl-1-methylcyclohexane.- 4.15 Write a structural isomer of methylcyclooctane that has a nine-membered ring; a six-membered ring; a seven-membered ring, and then name all three compounds.
- 4.16 Draw the structure of 1-chloro-3-ethyl-4,5,6-trimethylcyclononane.
A subtle naming problem arises when an acyclic carbon chain is attached to a cyclic alkane. Is the molecule named as a cyclic alkane with a substituent or as an acyclic chain with a cyclic substituent? The IUPAC rules state that a hydrocarbon with a small ring attached to a long chain is named as a derivative of the acyclic hydrocarbon. A hydrocarbon with a small alkyl chain attached to a large ring is generally named as a derivative of the cyclic hydrocarbon. A small ring is usually defined as three to six carbon atoms and a large ring is usually defined as ≥ seven carbon atoms . Therefore, make an assumption. If the number of carbon atoms in the longest acyclic carbon chain is six carbon atoms or less, the compound is named as a cyclic alkane, and the chain is treated as a substituent. If the longest acyclic chain is seven carbons or greater, the molecule is named as an acyclic alkane, with a cyclic substituent. Note that if a ring is named as a substituent, the -ane is dropped and replaced with -yl. Therefore, a cyclopropane unit treated as a substituent is cyclopropyl, a cyclobutane substituent is cyclobutyl, a cyclopentane substituent is cyclopentyl, and so on. Using this rule, the two compounds shown are 1-cyclopentyloctane and pentylcyclooctane.- 4.17 Give the IUPAC name for the following compound.
4.5 The Acid or Base Properties of Alkanes
Acid-base theory is used to examine the chemistry of organic molecules throughout this book, so it is reasonable to ask if an alkane is an acid or a base. All electrons in an alkane are “tied up” in covalent bonds, so there are no electrons to donate. In other words, an alkane does not react as a base! If the C—H unit in methane loses a proton as an acid, the conjugate base would be the methide anion, CH3 - , as shown in Figure 4.4 . The Ka for removing the hydrogen atom in an alkane is estimated to be < 10-40 so the pKa is >40. An alkane is therefore a very weak acid and no base has been discussed thus far that is strong enough to remove a proton from an alkane. If methide were to form, it would be a remarkably strong base, very reactive and an unstable entity. Alkanes are not used as acids in this book. However, identifying the pKa
eBook - ePubOrganic Chemistry
Fundamentals and Concepts
- John M. McIntosh(Author)
- 2022(Publication Date)
- De Gruyter(Publisher)
The time of changeover from one system to another is not short. It is very common to have more than one [sometimes several!] systems in use simultaneously. This is particularly true of stereochemical nomenclature. As noted in Chapter 2, the old way of denoting the stereochemistry of alkenes is by the use of the words cis and trans. When that system was introduced, it was noted that another system which is more generally applicable to alkenes and also is very useful in other, more complex systems would be introduced later. The time has come for this to happen. The chronology of the introduction of this new system is important. It was originally designed to cope with a completely different stereochemical problem and was subsequently expanded to apply to the stereochemistry of alkenes. Nevertheless, the subject will be introduced to you in reverse order. The Cahn–Ingold–Prelog System (CIP) The principle ideas behind this method of describing stereochemistry of alkenes are extremely simple. It consists of three steps. Divide the alkene in two by a line perpendicular to the double bond and through its center. On the basis of the Sequence Rules, assign priorities (importance) to the two substituents attached to each sp 2 -hybridized carbon. Put the molecule back together and determine if the highest priority group on both sp 2 carbons are on the same side or opposite sides of the molecule. If the former is true, the stereochemical descriptor Z is used, but if the latter is the case, the stereochemical descriptor E is used. To illustrate, consider the following. The molecule 1-bromo-1-chloro-propene can be divided into two halves as shown [Step #1]. The priorities are assigned on the basis of the Sequence Rules as shown [Rule #2]. The two highest priority groups, Fig
- David R. Klein(Author)
- 2017(Publication Date)
- Wiley(Publisher)
108 CHAPTER 4 4.10. For each compound, we assign its name in the following way: First identify the parent, then the substituents, and then assign locants (the final step, arranging the substituents alphabetically, is not needed for any of these examples). In each case, use commas to separate numbers from each other, and use hyphens to separate letters from numbers. (a) 2,2-dimethylundecane (b) 2-methyldodecane (c) 2,2-dimethyloctane (d) butylcyclohexane 4.11. For each of the following compounds, we assign its name via a four-step process: First identify the parent, then the substituents, then assign locants, and finally, arrange the substituents alphabetically. When assigning locants, make sure to start at a bridgehead and continue numbering along the longest path to the second bridgehead. Then continue assigning locants along the second longest path, and then finally, along the shortest path that connects the two bridgehead positions. (a) 4-ethyl-1-methylbicyclo[3.2.1]octane (b) 2,2,5,7-tetramethylbicyclo[4.2.0]octane (c) 2,7,7-trimethylbicyclo[4.2.2]decane (d) 3-sec-butyl-2-methylbicyclo[3.1.0]hexane (e) 2,2-dimethylbicyclo[2.2.2]octane 4.12. (a) The name indicates a bicyclic parent with two methyl groups at C2 and two methyl groups at C3, as shown: (b) The name indicates a bicyclic parent with two ethyl groups at C8, as shown: (c) The name indicates a bicyclic parent with an isopropyl group at C3, as shown: 4.13. The bicyclic parent contains eight carbon atoms (highlighted below). There are two carbon atoms in each of the three possible paths that connect the bridgehead carbons, so this bicyclic parent is bicyclo[2.2.2.]octane.
eBook - ePub- Robert J. Ouellette, J. David Rawn(Authors)
- 2015(Publication Date)
- Elsevier(Publisher)
Table 3.2 ). Many of these possible isomers have never been found in petroleum or produced in a chemistry laboratory, but each could be made in the laboratory. A system for naming the many isomeric alkanes is clearly necessary.Table 3.2 Number of Alkane IsomersMolecular Formula Number of Isomers CH4 1 C2 H6 1 C3 H8 1 C4 H10 2 C5 H12 3 C6 H14 5 C7 H16 9 C8 H18 18 C9 H20 35 C10 H22 75 C20 H42 336,319 C30 H62 4,111,846,763 C40 H82 62,491,178,805,831 IUPAC Rules for Naming Alkanes
Alkanes and other organic compounds are named by the rules set forth by the International Union of Pure and Applied Chemistry (IUPAC). When these rules are followed, every chemical compound has a unique name. The IUPAC name consists of three parts: prefix, parent, and suffix.The parent is the longest continuous carbon chain in a molecule that contains the functional group. The suffix identifies the functional group for most classes of organic compounds. A parent alkane has the ending -ane . Some functional groups, such as the halogens, are identified in the prefix. For example, the prefixes chloro and bromo identify chlorine and bromine. The prefix also indicates the identity and location of any branching alkyl groups. An alkane that has “lost” one hydrogen atom is called an alkyl group. Alkyl groups are named by replacing the -ane ending of an alkane with -yl . The parent name of CH4 is methane. Thus, CH3 – is a methyl group. The parent name of C2 H6 is ethane, so CH3 CH2
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
