| QuestionsAnswersExplanation21. Which type of reaction occurs when nonmetal atoms become negative nonmetal ions? A. oxidation Show Once equilibrium is reached, which statement is accurate? A. The concentration of Ag+(aq) is greater than the concentration of Cl–(aq). equilibrium rates are equal concentrations constant 23. Which structural formula correctly represents a hydrocarbon molecule?A.  B. C. D. H has 1 O has 2 24. Given the structural formulas for two organic compounds:The differences in their physical and chemical properties are primarily due to their A. number of carbon atoms A. B. C. D. Note A is pentane, not an isomer of 26. The bonds in the compound MgSO4 can be described asA. ionic, only MgSO4 is ionic so there is both 27. Given the reaction:Which statement correctly describes what occurs when this reaction takes place in a closed system? A. Atoms of Zn(s) lose electrons and are oxidized. charge went up...oxidation it is oxidized by losing electrons LEO GER 28. When the pH of a solution changes from a pH of 5 to a pH of 3, the hydronium ion concentration isA. 0.01 of the original content 5 to 3 is 100 times more H3O+ A. Ca2+ ions as the only positive ions in solution acids hydronium or hydrogen ions 30. Which reaction occurs when hydrogen ions react with hydroxide ions to form water?A. substitution neutralization \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)
Learning Objectives
There is free rotation about the carbon-to-carbon single bonds (C–C) in alkanes. In contrast, the structure of alkenes requires that the carbon atoms of a double bond and the two atoms bonded to each carbon atom all lie in a single plane, and that each doubly bonded carbon atom lies in the center of a triangle. This part of the molecule’s structure is rigid; rotation about doubly bonded carbon atoms is not possible without rupturing the bond. Look at the two chlorinated hydrocarbons in Figure \(\PageIndex{1}\). In 1,2-dichloroethane (part (a) of Figure \(\PageIndex{1}\)), there is free rotation about the C–C bond. The two models shown represent exactly the same molecule; they are not isomers. You can draw structural formulas that look different, but if you bear in mind the possibility of this free rotation about single bonds, you should recognize that these two structures represent the same molecule: In 1,2-dichloroethene (Figure \(\PageIndex{1b}\)), however, restricted rotation about the double bond means that the relative positions of substituent groups above or below the double bond become significant. This leads to a special kind of isomerism. The isomer in which the two chlorine (Cl) atoms lie on the same side of the molecule is called the cis isomer (Latin cis, meaning “on this side”) and is named cis-1,2-dichloroethene. The isomer with the two Cl atoms on opposite sides of the molecule is the trans isomer (Latin trans, meaning “across”) and is named trans-1,2-dichloroethene. These two compounds are cis-trans isomers (or geometric isomers), compounds that have different configurations (groups permanently in different places in space) because of the presence of a rigid structure in their molecule. Consider the alkene with the condensed structural formula CH3CH=CHCH3. We could name it 2-butene, but there are actually two such compounds; the double bond results in cis-trans isomerism (Figure \(\PageIndex{2}\)). Cis-2-butene has both methyl groups on the same side of the molecule. Trans-2-butene has the methyl groups on opposite sides of the molecule. Their structural formulas are as follows: Figure \(\PageIndex{3}\): Models of (left) Cis-2-Butene and (right) Trans-2-Butene. Note, however, that the presence of a double bond does not necessarily lead to cis-trans isomerism (Figure \(\PageIndex{4}\)). We can draw two seemingly different propenes: Figure \(\PageIndex{4}\): Different views of the propene molecule (flip vertically). These are not isomers. However, these two structures are not really different from each other. If you could pick up either molecule from the page and flip it over top to bottom, you would see that the two formulas are identical. Thus there are two requirements for cis-trans isomerism:
In these propene structures, the second requirement for cis-trans isomerism is not fulfilled. One of the doubly bonded carbon atoms does have two different groups attached, but the rules require that both carbon atoms have two different groups. In general, the following statements hold true in cis-trans isomerism:
Advanced Note: E/Z IsomerizationIf a molecule has a C=C bond with one non-hydrogen group attached to each of the carbons, cis/trans nomenclature descried above is enough to describe it. However, if you have three different groups (or four), then the cis/trans approach is insufficient to describe the different isomers, since we do not know which two of the three groups are being described. For example, if you have a C=C bond, with a methyl group and a bromine on one carbon , and an ethyl group on the other, it is neither trans nor cis, since it is not clear whether the ethyl group is trans to the bromine or the methyl. This is addressed with a more advanced E,Z Convention [E] [E] [E] discussed elsewhere. Cis-trans isomerism also occurs in cyclic compounds. In ring structures, groups are unable to rotate about any of the ring carbon–carbon bonds. Therefore, groups can be either on the same side of the ring (cis) or on opposite sides of the ring (trans). For our purposes here, we represent all cycloalkanes as planar structures, and we indicate the positions of the groups, either above or below the plane of the ring. Example \(\PageIndex{1}\)Which compounds can exist as cis-trans (geometric) isomers? Draw them.
Solution All four structures have a double bond and thus meet rule 1 for cis-trans isomerism.
Exercise \(\PageIndex{1}\)Which compounds can exist as cis-trans isomers? Draw them.
Key Takeaway
This page titled 13.2: Cis-Trans Isomers (Geometric Isomers) is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by Anonymous via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request. Which structural formula represents a molecule that is not an isomer of pentane?2003 August Chemistry Regents Exam #21-30. Which of the following is not an isomer of pentane?3,3 dimethyl butane is a 6 carbon structure so it cannot be an isomer for pentane.
What are the 5 isomers of pentane?Pentane is an alkane with the chemical formula C5H12. The three structural isomers of pentane are n-pentane, isopentane, and neopentane. Although these three similar compounds are often sold as a mixture of the three, the isomers have different boiling and melting points.
How many structural isomers are possible for pentane ___?So, there are three structural isomers of Pentane.
|
Which structural formula represents a molecule that is not an isomer of pentane A B C D?
Related Posts
Copyright © 2024 SignalDuo Inc.
