3 deleted 13 characters in body edited Jan 29 '18 at 22:19 orthocresol♦ 42.8k77 gold badges133133 silver badges263263 bronze badges Maybe my answer concerning the question why aniline is considered aromatic might help a bit. There I describe that groups that are cross-conjugated with the aromatic ring are not included into the "Huckel"Hückel-count" and give some arguments why this is so.  A similar argument would apply here: The keto group is cross-conjugated with the ring's $$\pi$$ systemπ-system but in a different way than the amino group is in aniline because the carbonyl carbon is part of the ring. So, the role of the keto group's π system is only to act as a bridge between the $$\ce{C=C}$$ $$\pi$$ orbitalsπ-orbitals so that the ring is "closed". Thus, you wouldn't count the keto group's electrons but only the $$\ce{C=C}$$ $$\pi$$ electronsπ-electrons. And this would lead to the conclusion that your cyclic ketone will be aromatic if it really is flat (that will have to be checked by NMR or other methods) because there are 6 $$\pi$$ electronsπ-electrons in the ring. Maybe my answer concerning the question why aniline is considered aromatic might help a bit. There I describe that groups that are cross-conjugated with the aromatic ring are not included into the "Huckel-count" and give some arguments why this is so. A similar argument would apply here: The keto group is cross-conjugated with the ring's $$\pi$$ system but in a different way than the amino group is in aniline because the carbonyl carbon is part of the ring. So, the role of the keto group's π system is only to act as a bridge between the $$\ce{C=C}$$ $$\pi$$ orbitals so that the ring is "closed". Thus, you wouldn't count the keto group's electrons but only the $$\ce{C=C}$$ $$\pi$$ electrons. And this would lead to the conclusion that your cyclic ketone will be aromatic if it really is flat (that will have to be checked by NMR or other methods) because there are 6 $$\pi$$ electrons in the ring. Maybe my answer concerning the question why aniline is considered aromatic might help a bit. There I describe that groups that are cross-conjugated with the aromatic ring are not included into the "Hückel-count" and give some arguments why this is so.  A similar argument would apply here: The keto group is cross-conjugated with the ring's π-system but in a different way than the amino group is in aniline because the carbonyl carbon is part of the ring. So, the role of the keto group's π system is only to act as a bridge between the $$\ce{C=C}$$ π-orbitals so that the ring is "closed". Thus, you wouldn't count the keto group's electrons but only the $$\ce{C=C}$$ π-electrons. And this would lead to the conclusion that your cyclic ketone will be aromatic if it really is flat (that will have to be checked by NMR or other methods) because there are 6 π-electrons in the ring. 2 replaced http://chemistry.stackexchange.com/ with https://chemistry.stackexchange.com/ edited Apr 13 '17 at 12:57 Maybe my answermy answer concerning the question why aniline is considered aromatic might help a bit. There I describe that groups that are cross-conjugated with the aromatic ring are not included into the "Huckel-count" and give some arguments why this is so. A similar argument would apply here: The keto group is cross-conjugated with the ring's $$\pi$$ system but in a different way than the amino group is in aniline because the carbonyl carbon is part of the ring. So, the role of the keto group's π system is only to act as a bridge between the $$\ce{C=C}$$ $$\pi$$ orbitals so that the ring is "closed". Thus, you wouldn't count the keto group's electrons but only the $$\ce{C=C}$$ $$\pi$$ electrons. And this would lead to the conclusion that your cyclic ketone will be aromatic if it really is flat (that will have to be checked by NMR or other methods) because there are 6 $$\pi$$ electrons in the ring. Maybe my answer concerning the question why aniline is considered aromatic might help a bit. There I describe that groups that are cross-conjugated with the aromatic ring are not included into the "Huckel-count" and give some arguments why this is so. A similar argument would apply here: The keto group is cross-conjugated with the ring's $$\pi$$ system but in a different way than the amino group is in aniline because the carbonyl carbon is part of the ring. So, the role of the keto group's π system is only to act as a bridge between the $$\ce{C=C}$$ $$\pi$$ orbitals so that the ring is "closed". Thus, you wouldn't count the keto group's electrons but only the $$\ce{C=C}$$ $$\pi$$ electrons. And this would lead to the conclusion that your cyclic ketone will be aromatic if it really is flat (that will have to be checked by NMR or other methods) because there are 6 $$\pi$$ electrons in the ring. Maybe my answer concerning the question why aniline is considered aromatic might help a bit. There I describe that groups that are cross-conjugated with the aromatic ring are not included into the "Huckel-count" and give some arguments why this is so. A similar argument would apply here: The keto group is cross-conjugated with the ring's $$\pi$$ system but in a different way than the amino group is in aniline because the carbonyl carbon is part of the ring. So, the role of the keto group's π system is only to act as a bridge between the $$\ce{C=C}$$ $$\pi$$ orbitals so that the ring is "closed". Thus, you wouldn't count the keto group's electrons but only the $$\ce{C=C}$$ $$\pi$$ electrons. And this would lead to the conclusion that your cyclic ketone will be aromatic if it really is flat (that will have to be checked by NMR or other methods) because there are 6 $$\pi$$ electrons in the ring. 1 answered Dec 4 '14 at 4:44 Philipp 15.1k22 gold badges5858 silver badges105105 bronze badges Maybe my answer concerning the question why aniline is considered aromatic might help a bit. There I describe that groups that are cross-conjugated with the aromatic ring are not included into the "Huckel-count" and give some arguments why this is so. A similar argument would apply here: The keto group is cross-conjugated with the ring's $$\pi$$ system but in a different way than the amino group is in aniline because the carbonyl carbon is part of the ring. So, the role of the keto group's π system is only to act as a bridge between the $$\ce{C=C}$$ $$\pi$$ orbitals so that the ring is "closed". Thus, you wouldn't count the keto group's electrons but only the $$\ce{C=C}$$ $$\pi$$ electrons. And this would lead to the conclusion that your cyclic ketone will be aromatic if it really is flat (that will have to be checked by NMR or other methods) because there are 6 $$\pi$$ electrons in the ring.