{"id":193369,"date":"2025-02-19T10:49:16","date_gmt":"2025-02-19T10:49:16","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=193369"},"modified":"2025-02-19T10:49:18","modified_gmt":"2025-02-19T10:49:18","slug":"interpret-the-ir-spectrum-for-benzoin-benzil-and-benzilic-acid","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/02\/19\/interpret-the-ir-spectrum-for-benzoin-benzil-and-benzilic-acid\/","title":{"rendered":"interpret the IR spectrum for benzoin, benzil and benzilic acid"},"content":{"rendered":"\n

interpret the IR spectrum for benzoin, benzil and benzilic acid. draw out compound on the corresponding spectrum and indicate the specific absorbance ( not the ranges from correlation table)for each type of bond. focus especially on amy OH bonds . some of the hydrogen bonding hroups display sharper than normal absorbance . Explain Why.(Hint -draw the molecules carefully with lots of detail).<\/p>\n\n\n\n

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

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

Benzoin:<\/h3>\n\n\n\n

Benzoin (C6H5CHOHCO-C6H5) contains a hydroxyl group (-OH) and a carbonyl group (C=O). In the IR spectrum, look for:<\/p>\n\n\n\n

    \n
  • Hydroxyl group (OH)<\/strong>: A broad, strong absorption typically appears around 3200-3550 cm^-1<\/strong>. This is due to the O-H stretch, and it may show broadening due to hydrogen bonding.<\/li>\n\n\n\n
  • Carbonyl group (C=O)<\/strong>: A sharp, strong absorption will appear around 1700 cm^-1<\/strong>, characteristic of the carbonyl stretch.<\/li>\n<\/ul>\n\n\n\n

    The hydroxyl group in benzoin might show sharper absorbance due to hydrogen bonding, which can increase the intensity and sharpness of the O-H stretch compared to compounds with non-hydrogen-bonded hydroxyl groups.<\/p>\n\n\n\n

    Benzil:<\/h3>\n\n\n\n

    Benzil (C6H5COCOC6H5) is a diketone with two carbonyl groups. In the IR spectrum, expect:<\/p>\n\n\n\n

      \n
    • Carbonyl groups (C=O)<\/strong>: Two strong absorptions will appear around 1700 cm^-1<\/strong> (one for each carbonyl). The exact location can vary slightly based on conjugation.<\/li>\n\n\n\n
    • There are no OH groups in benzil, so the spectrum will lack the broad O-H stretch.<\/li>\n<\/ul>\n\n\n\n

      Benzilic Acid:<\/h3>\n\n\n\n

      Benzilic acid (C6H5C(OH)2COOH) contains both a hydroxyl group and a carboxylic acid group. In the IR spectrum:<\/p>\n\n\n\n

        \n
      • Carboxylic acid (COOH)<\/strong>: The O-H stretch appears around 2500-3300 cm^-1<\/strong> but is broad and overlaps with the C-H stretches. The C=O stretch for the carboxyl group typically appears around 1700 cm^-1<\/strong>.<\/li>\n\n\n\n
      • Hydroxyl group (OH)<\/strong>: Like benzoin, this stretch is broad but can appear sharper if hydrogen bonding is involved.<\/li>\n<\/ul>\n\n\n\n

        Explanation of Sharp Absorbance:<\/h3>\n\n\n\n

        Hydrogen bonding influences the O-H stretch. When the hydroxyl group is involved in hydrogen bonding (like in carboxylic acids or phenols), it broadens the absorption and increases its intensity. In some cases, this can cause the O-H stretch to appear sharper than typical non-hydrogen-bonded OH stretches. The exact effect can depend on the strength and extent of the hydrogen bonding in the sample.<\/p>\n\n\n\n

        Now, let me generate the molecular structures for benzoin, benzil, and benzilic acid to visualize them alongside the explanations.<\/p>\n\n\n\n

        Here are the molecular structures for benzoin<\/strong>, benzil<\/strong>, and benzilic acid<\/strong>. The hydroxyl (-OH), carboxyl (-COOH), and carbonyl (C=O) groups are clearly shown for each compound.<\/p>\n\n\n\n

        Key Points:<\/h3>\n\n\n\n
          \n
        • Benzoin<\/strong>: Contains a hydroxyl (-OH) group and a carbonyl group. The hydroxyl group’s IR absorption can be sharp due to hydrogen bonding.<\/li>\n\n\n\n
        • Benzil<\/strong>: A diketone, so only the two carbonyl stretches are present.<\/li>\n\n\n\n
        • Benzilic acid<\/strong>: Has both a hydroxyl group and a carboxyl group. The IR spectrum for this compound will show broadening in the O-H region due to the carboxyl group\u2019s hydrogen bonding.<\/li>\n<\/ul>\n\n\n\n

          Hydrogen bonding in these compounds, especially with the hydroxyl and carboxyl groups, is a critical factor that sharpens and intensifies the OH stretch absorption in the IR spectrum.<\/p>\n","protected":false},"excerpt":{"rendered":"

          interpret the IR spectrum for benzoin, benzil and benzilic acid. draw out compound on the corresponding spectrum and indicate the specific absorbance ( not the ranges from correlation table)for each type of bond. focus especially on amy OH bonds . some of the hydrogen bonding hroups display sharper than normal absorbance . Explain Why.(Hint -draw […]<\/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-193369","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/193369","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=193369"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/193369\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=193369"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=193369"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=193369"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}