{"id":207362,"date":"2025-04-21T15:49:09","date_gmt":"2025-04-21T15:49:09","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=207362"},"modified":"2025-04-21T15:49:11","modified_gmt":"2025-04-21T15:49:11","slug":"discuss-the-principle-of-ir-spectroscopy","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/04\/21\/discuss-the-principle-of-ir-spectroscopy\/","title":{"rendered":"Discuss the principle of IR spectroscopy"},"content":{"rendered":"\n<p>Discuss the principle of IR spectroscopy. How will you distinguish between the following pairs of compounds on the basis of IR spectroscopy:<\/p>\n\n\n\n<p>(a) Ethyl alcohol and diethyl ether<\/p>\n\n\n\n<p>(b) Acetic acid and ethyl acetate<\/p>\n\n\n\n<p><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-ast-global-color-6-color\"><strong>The correct answer and explanation is :<\/strong><\/mark><\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Principle of IR Spectroscopy:<\/h3>\n\n\n\n<p>Infrared (IR) spectroscopy is an analytical technique used to identify and study chemicals based on how molecules absorb infrared light. When IR radiation passes through a compound, certain frequencies are absorbed by the molecule, causing specific bonds to vibrate (stretch, bend, or twist). These vibrations depend on the types of atoms involved and the nature of the chemical bonds. The resulting spectrum is a plot of absorption (or transmittance) versus frequency (usually in cm\u207b\u00b9), and each functional group shows characteristic absorption bands.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">(a) <strong>Ethyl alcohol (CH\u2083CH\u2082OH) vs. Diethyl ether (CH\u2083CH\u2082OCH\u2082CH\u2083):<\/strong><\/h3>\n\n\n\n<p>To distinguish between these compounds using IR spectroscopy:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Ethyl alcohol<\/strong>:<\/li>\n\n\n\n<li>Shows a <strong>broad O\u2013H stretching<\/strong> band around <strong>3200\u20133600 cm\u207b\u00b9<\/strong>, due to hydrogen bonding.<\/li>\n\n\n\n<li>C\u2013H stretching around <strong>2900 cm\u207b\u00b9<\/strong>.<\/li>\n\n\n\n<li>C\u2013O stretching around <strong>1000\u20131100 cm\u207b\u00b9<\/strong>.<\/li>\n\n\n\n<li><strong>Diethyl ether<\/strong>:<\/li>\n\n\n\n<li>Lacks an O\u2013H group, so <strong>no broad O\u2013H stretch<\/strong>.<\/li>\n\n\n\n<li>Shows C\u2013H stretches (~2900 cm\u207b\u00b9).<\/li>\n\n\n\n<li>Shows <strong>C\u2013O\u2013C asymmetric and symmetric stretches<\/strong> in the <strong>1050\u20131150 cm\u207b\u00b9<\/strong> region.<\/li>\n<\/ul>\n\n\n\n<p>\ud83d\udc49 <strong>Key difference<\/strong>: Presence of <strong>broad O\u2013H stretch<\/strong> in alcohol, <strong>absent<\/strong> in ether.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">(b) <strong>Acetic acid (CH\u2083COOH) vs. Ethyl acetate (CH\u2083COOCH\u2082CH\u2083):<\/strong><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Acetic acid<\/strong>:<\/li>\n\n\n\n<li><strong>Broad O\u2013H stretch<\/strong> around <strong>2500\u20133300 cm\u207b\u00b9<\/strong>.<\/li>\n\n\n\n<li>Sharp <strong>C=O stretch<\/strong> of carboxylic acid near <strong>1700\u20131725 cm\u207b\u00b9<\/strong>.<\/li>\n\n\n\n<li><strong>O\u2013H bending<\/strong> near <strong>1400 cm\u207b\u00b9<\/strong>.<\/li>\n\n\n\n<li><strong>Ethyl acetate<\/strong>:<\/li>\n\n\n\n<li>No O\u2013H stretch (no carboxylic acid group).<\/li>\n\n\n\n<li>Shows <strong>C=O stretch<\/strong> of ester near <strong>1735\u20131750 cm\u207b\u00b9<\/strong>.<\/li>\n\n\n\n<li><strong>C\u2013O stretches<\/strong> in the <strong>1050\u20131300 cm\u207b\u00b9<\/strong> range.<\/li>\n<\/ul>\n\n\n\n<p>\ud83d\udc49 <strong>Key difference<\/strong>: <strong>Broader O\u2013H stretch<\/strong> and slightly <strong>lower C=O frequency<\/strong> in acetic acid vs. <strong>sharper, higher-frequency C=O<\/strong> in ester.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">Summary:<\/h3>\n\n\n\n<p>IR spectroscopy distinguishes compounds by identifying functional groups. Alcohols and carboxylic acids show broad O\u2013H stretches, while ethers and esters do not. Carbonyl stretching frequencies also help differentiate between acids and esters.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img decoding=\"async\" src=\"https:\/\/learnexams.com\/blog\/wp-content\/uploads\/2025\/04\/image-228.png\" alt=\"\" class=\"wp-image-207364\"\/><\/figure>\n","protected":false},"excerpt":{"rendered":"<p>Discuss the principle of IR spectroscopy. How will you distinguish between the following pairs of compounds on the basis of IR spectroscopy: (a) Ethyl alcohol and diethyl ether (b) Acetic acid and ethyl acetate The correct answer and explanation is : Principle of IR Spectroscopy: Infrared (IR) spectroscopy is an analytical technique used to identify [&hellip;]<\/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-207362","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/207362","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=207362"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/207362\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=207362"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=207362"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=207362"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}