{"id":226758,"date":"2025-06-05T14:36:40","date_gmt":"2025-06-05T14:36:40","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=226758"},"modified":"2025-06-05T14:36:43","modified_gmt":"2025-06-05T14:36:43","slug":"define-whether-the-following-vibrational-modes-of-co2-and-no2-are-ir-active-or-not","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/06\/05\/define-whether-the-following-vibrational-modes-of-co2-and-no2-are-ir-active-or-not\/","title":{"rendered":"Define whether the following vibrational modes of CO2 and NO2 are IR active or not."},"content":{"rendered":"\n

Define whether the following vibrational modes of CO2 and NO2 are IR active or not. A weak signal is considered active: Symmetric stretch: 0=C=0 Asymmetric stretch: 0-C=0 In-plane bending: 0 Out-of-plane bending: 0<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

The Correct Answer and Explanation is:<\/mark><\/strong><\/p>\n\n\n\n

To determine whether vibrational modes of CO\u2082 and NO\u2082\u207b are IR active, we apply the principle that a vibrational mode is IR active if it results in a change in the dipole moment of the molecule. Here’s the correct classification for each vibrational mode shown in the image:<\/p>\n\n\n\n

\n\n\n\n

CO\u2082 (Carbon Dioxide)<\/strong><\/h3>\n\n\n\n
    \n
  1. Symmetric Stretch:<\/strong>IR Inactive<\/strong>\n
      \n
    • In this mode, both O atoms move simultaneously toward and away from the C atom.<\/li>\n\n\n\n
    • Since CO\u2082 is a linear and symmetric molecule, this motion does not change the dipole moment (which remains zero), so it is IR inactive<\/strong>.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
    • Asymmetric Stretch:<\/strong>IR Active<\/strong>\n
        \n
      • In this mode, one O atom moves toward the C while the other moves away.<\/li>\n\n\n\n
      • This creates a temporary dipole moment as the charge distribution becomes asymmetric. Therefore, it is IR active<\/strong>.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
      • In-Plane Bending:<\/strong>IR Active<\/strong>\n
          \n
        • The O atoms move perpendicular to the linear axis of the molecule.<\/li>\n\n\n\n
        • This bending distorts the symmetry and creates a change in dipole moment, making it IR active<\/strong>.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n\n\n\n
          \n\n\n\n

          NO\u2082\u207b (Nitrite Ion)<\/strong><\/h3>\n\n\n\n
            \n
          1. Symmetric Stretch:<\/strong>IR Active (weak)<\/strong>\n
              \n
            • Though the molecule is bent and not linear like CO\u2082, the symmetric stretch causes a slight dipole moment fluctuation.<\/li>\n\n\n\n
            • Hence, it is weakly IR active<\/strong>.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
            • Asymmetric Stretch:<\/strong>IR Active<\/strong>\n
                \n
              • The two N\u2013O bonds stretch unequally, leading to a considerable change in dipole moment.<\/li>\n\n\n\n
              • This motion is strongly IR active<\/strong>.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
              • In-Plane Bending:<\/strong>IR Active<\/strong>\n
                  \n
                • Similar to CO\u2082, the bending motion in NO\u2082\u207b changes the dipole moment, making it IR active<\/strong>.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n\n\n\n
                  \n\n\n\n

                  Summary Table:<\/h3>\n\n\n\n
                  Vibrational Mode<\/th>CO\u2082 IR Activity<\/th>NO\u2082\u207b IR Activity<\/th><\/tr><\/thead>
                  Symmetric Stretch<\/td>No<\/td>Yes (weak)<\/td><\/tr>
                  Asymmetric Stretch<\/td>Yes<\/td>Yes<\/td><\/tr>
                  In-Plane Bending<\/td>Yes<\/td>Yes<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

                  These assignments reflect how molecular symmetry and changes in dipole moment determine IR activity.<\/p>\n\n\n\n

                  \"\"<\/figure>\n","protected":false},"excerpt":{"rendered":"

                  Define whether the following vibrational modes of CO2 and NO2 are IR active or not. A weak signal is considered active: Symmetric stretch: 0=C=0 Asymmetric stretch: 0-C=0 In-plane bending: 0 Out-of-plane bending: 0 The Correct Answer and Explanation is: To determine whether vibrational modes of CO\u2082 and NO\u2082\u207b are IR active, we apply the principle […]<\/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-226758","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/226758","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=226758"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/226758\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=226758"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=226758"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=226758"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}