Textbook Question
Which of the following compounds show cis-trans isomerism? Draw the cis and trans isomers of those that do.
(a) CHF=CHF
(b) F2C=CH2
(c) CH2=CH–CH2–CH3
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4. Alkanes and Cycloalkanes
Cis vs Trans
4:25 minutesProblem 8b
Textbook Question
Assign relative priorities to each set of substituents:
b. -CH2CH2OH, -OH, -CH2Cl, -CH=CH2
Verified step by step guidance1
Step 1: Understand the concept of assigning priorities using the Cahn-Ingold-Prelog (CIP) priority rules. These rules are based on atomic number, connectivity, and the presence of double or triple bonds. Higher atomic numbers take precedence, and if the first atom is the same, you move outward to the next atoms in the substituent chain.
Step 2: Analyze the substituents provided: -CH2CH2OH, -OH, -CH2Cl, and -CH=CH2. Begin by comparing the first atom directly attached to the main chain for each substituent. For -CH2CH2OH, -CH2Cl, and -CH=CH2, the first atom is carbon (C), while for -OH, the first atom is oxygen (O). Since oxygen has a higher atomic number (8) than carbon (6), -OH is assigned the highest priority.
Step 3: For the remaining substituents (-CH2CH2OH, -CH2Cl, -CH=CH2), compare the atoms directly bonded to the first carbon. For -CH2CH2OH, the second atom is another carbon bonded to an oxygen (O). For -CH2Cl, the second atom is chlorine (Cl). For -CH=CH2, the second atom is carbon involved in a double bond. Chlorine has the highest atomic number among these, so -CH2Cl is assigned the next highest priority.
Step 4: Compare the remaining substituents (-CH2CH2OH and -CH=CH2). For -CH2CH2OH, the second carbon is bonded to an oxygen atom, while for -CH=CH2, the second carbon is part of a double bond. A double bond is treated as if the carbon is bonded to two additional carbons, which increases its priority. Therefore, -CH=CH2 is assigned the next highest priority.
Step 5: Assign the lowest priority to -CH2CH2OH, as its second carbon is bonded to an oxygen atom, which is less significant in priority compared to the double bond in -CH=CH2. The final order of priorities is: 1) -OH, 2) -CH2Cl, 3) -CH=CH2, 4) -CH2CH2OH.
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Video duration:
4mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Substituent Priority in Organic Chemistry
In organic chemistry, substituent priority is determined by the Cahn-Ingold-Prelog (CIP) priority rules, which assign priorities based on atomic number and connectivity. Higher atomic numbers take precedence, and if two substituents are identical, the next atoms in the chain are considered. This is crucial for determining stereochemistry and reactivity in organic molecules.
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Functional Groups
Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. In the given question, -OH (hydroxyl) and -CH2Cl (chloromethyl) are functional groups that influence the properties and reactivity of the compounds. Understanding these groups helps in predicting how different substituents will interact.
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Double Bonds and Their Impact
Double bonds, such as those found in alkenes like -CH=CH2, significantly affect the reactivity and stability of organic compounds. They introduce geometric isomerism and can influence the overall priority of substituents due to their electron-rich nature. Recognizing the presence of double bonds is essential for accurately assigning priorities among substituents.
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