היפרקוניוגציה

בכימיה, היפרקוניוגציה ("צימוד על") היא אינטראקציה מייצבת, תוצאה של אינטראקציה של אלקטרונים בקשר סיגמא (בדרך כלל C-H או C-C) עם אורביטל p לא-קושר או אורביטל π אנטי-קושר פנוי (או מלא חלקית) קרוב. האינטראקציה יוצרת אורביטל מולקולרי מורחב, שמביא לייצוב המערכת. היפרקוניוגציה יכולה להביא לייצוב קרבוקטיון, אך רק אלקטרונים בקשרים שהם בעמדת β לפחמן הטעון חיובית יכולים לסייע בכך. למשל כאשר פחמן קשור לקבוצת מתיל אזי האלקטרונים של קבוצת המתיל מסייעים ויוצרים היפרקוניוגציה בין הפחמן לבין קבוצת המתיל.

תופעת ההיפרקוניוגציה משמשת כהסבר למגוון תופעות כימיות, בהן האפקט האנומרי, אפקט גוש, המחסום הסיבובי של אתאן, אפקט הבטא-סיליקון, התדירות הוויברציונית של קבוצות קרבוניל אקסוציקליות, והיציבות היחסית של קרבוקטיונים מותמרים.

לפי מודלים קוונטיים, היפרקוניוגציה היא ההסבר הנכון להעדפה לקונפורמציית סטגרד, בניגוד לטיעון המקובל של הפרעה סטרית.[1][2]

ראו גם

קישורים חיצוניים

הערות שוליים

  1. ^ Hyperconjugation not steric repulsion leads to the staggered structure of ethane Pophristic, V. & Goodman, L. Nature 411, 565–568 (2001)Abstract
  2. ^ Chemistry: A new twist on molecular shape Frank Weinhold Nature 411, 539-541 (31 May 2001)
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