Ethylene glycol (HOCH2CH2OH), the major substance in antifreeze, has a normal boiling point of 198 \u00b0C. By comparison, ethyl alcohol (CH3CH2OH) boils at 78 \u00b0C at atmospheric pressure. Ethylene glycol dimethyl ether (CH3OCH2CH2OCH3) has a normal boiling point of 83 \u00b0C, and ethyl methyl ether (CH3CH2OCH3) has a normal boiling point of 11 \u00b0C.
a) Explain why replacement of a hydrogen on the oxygen by CH3 generally results in a lowering boiling point.
Note that part b) of this question follows below.
A By replacing the -OH group with an -OCH3 group, the molecule has lost its ability to form H-bonds.
B By replacing the -OH group with an -OCH3 group, the molecule has gained the ability to form more effective London dispersion forces.
C By replacing the -OH group with an -OCH3 group, the molecule has gained the ability to form H-bonds, which is the weakest of the IMF, replacing the stronger London dispersion forces and dipole-dipole intermolecular forces that were on the molecule before this change.
D This is a trick question. The boiling points should actually be swapped for ethylene glycol and ethylene glycol dimethyl ether, as well as the ethyl alcohol and ethyl methyl ether. Replacing the -OH group with an -OCH3 group should actually cause an increase in boiling point.<\/p>\n\n\n\n
The correct answer and explanation is :<\/strong><\/mark><\/p>\n\n\n\n Correct Answer: A<\/strong> Explanation:<\/strong><\/p>\n\n\n\n Boiling point is largely influenced by the strength of intermolecular forces (IMFs) within a substance. The stronger these forces, the more energy (in the form of heat) is required to break them and allow the molecules to escape into the gas phase.<\/p>\n\n\n\n Hydrogen bonding is one of the strongest types of IMFs. It occurs when a hydrogen atom is directly bonded to a highly electronegative atom like oxygen, nitrogen, or fluorine. In alcohols like ethyl alcohol (CH\u2083CH\u2082OH) and ethylene glycol (HOCH\u2082CH\u2082OH), the presence of -OH (hydroxyl) groups allows for strong hydrogen bonding between molecules. Ethylene glycol, with two<\/strong> -OH groups, forms extensive hydrogen bonding networks, which significantly raise its boiling point to 198 \u00b0C.<\/p>\n\n\n\n When a -OH group is replaced by a -OCH\u2083 (methoxy) group to form an ether, such as ethyl methyl ether or ethylene glycol dimethyl ether, the molecule can no longer donate hydrogen bonds (since it lacks the -OH hydrogen). While ethers still have a polar C\u2013O bond and can accept<\/strong> hydrogen bonds (e.g., from water), they cannot form hydrogen bonds among themselves<\/strong> the way alcohols can. This greatly reduces the overall strength of IMFs in the liquid phase, resulting in much lower boiling points<\/strong>.<\/p>\n\n\n\n For instance, ethyl methyl ether (CH\u2083CH\u2082OCH\u2083) has a boiling point of just 11 \u00b0C\u2014dramatically lower than ethyl alcohol (78 \u00b0C). The difference arises solely from the loss of hydrogen bonding capability upon replacing -OH with -OCH\u2083.<\/p>\n\n\n\n In short, the key factor<\/strong> in the boiling point difference is hydrogen bonding<\/strong>. Losing -OH groups and replacing them with -OCH\u2083 groups means losing the molecule\u2019s ability to form these strong intermolecular forces, thus lowering the boiling point.<\/p>\n","protected":false},"excerpt":{"rendered":" Ethylene glycol (HOCH2CH2OH), the major substance in antifreeze, has a normal boiling point of 198 \u00b0C. By comparison, ethyl alcohol (CH3CH2OH) boils at 78 \u00b0C at atmospheric pressure. Ethylene glycol dimethyl ether (CH3OCH2CH2OCH3) has a normal boiling point of 83 \u00b0C, and ethyl methyl ether (CH3CH2OCH3) has a normal boiling point of 11 \u00b0C.a) Explain […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[25],"tags":[],"class_list":["post-207695","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/207695","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/comments?post=207695"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/207695\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=207695"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=207695"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=207695"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
“By replacing the -OH group with an -OCH3 group, the molecule has lost its ability to form H-bonds.”<\/strong><\/p>\n\n\n\n
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