Ethers constitutional isomers

The constitutional isomer of ethanol dimethyl ether (CH3OCH3) IS a gas at room temperature Suggest an explanation for this observation I... 

Constitutional isomerism is not limited to alkanes—it occurs widely throughout organic chemistry. Constitutional isomers may have different carbon skeletons (as in isobutane and butane), different functional groups (as in ethanol and dimethyl ether), or different locations of a functional group along the chain (as in isopropylamine and propylamine). Regardless of the reason for the isomerism, constitutional isomers are always different compounds with different properties, but with the same formula. 

SAMPLE SOLUTION (a) Begin by considering the ways in which two carbons and one oxygen may be bonded. There are two possibilities C—C—O and C—O—C. Add the six hydrogens so that each carbon has four bonds and each oxygen two. There are two constitutional isomers ethyl alcohol and dimethyl ether. 

The first electrochemical reduction of these constitutional isomers occurs around —1.13 V v. Fc/Fc+ and they are anodically shifted by about 70-80 mV when complexed by either Na+ or K+. The anodic shift is due to the presence of the positive charge on the bound cation, as observed previously for the C60 trans-1 crown ether analog [30,55], Successive reductions of the fullerenocrowns are chemically irreversible, a consequence of retrocyclopropanation reactions, as will be described later in this chapter. 

Which of these two structures is correct Both of them satisfy the octet rule and neither has formal charges, so both are predicted to be of comparable stability. On the basis of what we have discussed so far, we cannot predict which is more stable. In fact, both of these compounds are quite stable and can be put in a bottle. But they are different compounds. Ethyl alcohol is the alcohol found in beverages. It is a liquid at room temperature. In contrast, dimethyl ether is a gas at room temperature and is quite poisonous. As was mentioned in Section 1.7, compounds such as these, with the same molecular formula but different arrangements of bonded atoms (different structures or different connectivities), are called constitutional isomers (or structural isomers). Constitutional isomerism is very common in organic compounds. This is another reason why it is necessary to show the structure of the compound under discussion rather than just the molecular formula. 

Isomers that have equal GTDs between corresponding atoms are classified as stereoisomers . Those with unequal GTDs between at least one pair of atoms are structural isomers also referred to as constitutional isomers . For example, in Figure 1, the GTD between the two carbon atoms in ethanol = 1, while in dimethyl ether GTD = 2. 

Ethanol and dimethyl ether are constitutional isomers because they have the same molecular formula, but the connectivity of their atoms is different. For example, ethanol has one C-C bond and one O-H bond, whereas dimethyl ether has two C-O bonds. A second class of isomers, called stereoisomers, is introduced in Section 4.13B. 

Constitutional isomers like butane and isobutane belong to the same family of compounds they are both alkanes. In contrast, constitutional isomers like CH3CH2OH and CH3OCH3 have different functional groups and belong to different families CH3CH2OH is an alcohol and CH3OCH3 is an ether. 

Problem 9.1 Draw all constitutional isomers having molecular formula C4H10O. Classify each compound as a 1 °, 2°, or 3° alcohol, or a symmetrical or unsymmetrical ether. 

Dimethyl ether (CH3OCH3) and ethanol (CH3CH2OH) are constitutional isomers, (a) Use Table 9.2 to calculate AH%n for the formation of each compound as a gas from methane and oxygen water vapor also forms, (b) State which reaction is more exothermic, (c) Calculate AH° for the conversion of ethanol to dimethyl ether. 

The constitution of a molecule (number of, kind of, and connectivities of atoms) may be represented by a two-dimensional map in which the interatomic linkages (bonds) are drawn as fines. There are two constitutional isomers that are represented by the molecular formula C2HgO ethanol and dimethyl ether. The differences in connectivities, which are not evident in the common constitutional inventory C2H6O, can be conveyed by typographical fine formulas (CH3CH2OH for etfianol and CH3OCH3 for dimethyl ether), or by structural representations (see Figure 2). As the number and kinds of atoms in substances increase, the number of constitutional isomers increases. 

Constitutional isomerism is defined as that type of isomerism (i.e., different structures corresponding to the same molecular formula) resulting from differences in vicinity relationships between atoms. Examples of pairs of constitutional isomers are -butane and isobutane [CCCC versus CC(C)C in Smiles notation], ethanol and dimethyl ether (CCO versus COC), 1 - and 2-methylbutene (C=CCC versus CC=CC), and 1- and 2-propanol [CCCO versus CC(0)C]. Constitutional isomerism is adequately accounted for in chemical graph theory by the adjacency or distance matrices, which consider only the vicinity relationships. ... 

Ans. This problem is not the same as Problem 13.23. The latter specified ethers with the formula C4H10O but this problem does not have that limitation. Alcohols and ethers are constitutional isomers of each other. The answer to this problem is the sum of the answers to Problems 13.5 (C4H jqO alcohols) and 13.23 (C4H,oO ethers). 

Different compounds that have the same molecular formula are classified as isomers Isomers can be either constitutional isomers (differ in connectivity) or stereoisomers (differ in arrangement of atoms in space). Constitutional isomers are also sometimes called structural isomers. Ethanol and dimethyl ether are constitutional isomers of each other. Stereoisomers will be introduced in Section 3.11. 

The effect of hydrogen bonding is illustrated dramatically by comparing the boiling points of ethanol (78 °C) and its constitutional isomer dimethyl ether ( — 24 °C). The difference in boiling points between these two compounds is due to the polar O — H group in the alcohol, which is capable of forming... 

In Section 10.2, we illustrated the importance of hydrogen bonding in alcohols by comparing the boiling points of ethanol (bp 78°C) and its constitutional isomer dimethyl ether (bp -24°C). By comparison, the boiling point of ethanethiol is 35 C and that of its constitutional isomer dimethyl sulfide is 37°C. 

Ethanol (CHjCHjOH) and dimethyl ether (CH3OCH3) are constitutional isomers. 

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